Keto Tuna Casserole

Name: Keto Tuna Casserole
Prep time: 15 min
Cook time: 15 min
Total time: 30 min
Ingredients: 2 5-ounce cans tuna in water (drained and flaked); 1/3 cup mayonnaise; 1 tablespoon Dijon mustard; 1/2 cup Gruyere cheese (shredded, divided); 1/4 cup red onion (minced); 1/4 teaspoon sea salt; 1/4 teaspoon black pepper; ¼ teaspoon cayenne pepper; ¼ cup parsley (chopped, for garnish)

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This delicious and filling keto tuna casserole has no noodles, but it has plenty of flavor!

Ready in just 30 minutes and made with simple everyday ingredients, this easy recipe is perfect for a weeknight dinner.

Keto tuna casserole is served in a white baking dish.

Canned tuna is one of my favorite ingredients. It's tasty, filling, and affordable. And just as important - I always have it on hand, making it the natural choice when the fridge is otherwise bare.

I use it to make tuna cakes and tuna salad. I also use it to make this keto tuna casserole. It's so good! It has no noodles, but you won't miss them. It's a lazy casserole - minimal chopping necessary. And it's ready fast, so it's perfect for weeknight dinners.

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Ingredients
Variations
Instructions
Expert Tip
Recipe FAQs
Reader Review
Serving Suggestions
Storing Leftovers
More Tuna Recipes
Foodie Newsletter
Recipe Card
Comments

Ingredients

This casserole is a delicious, filling, and well-seasoned mixture of canned tuna, chopped red onion, mayonnaise, and cheese, baked until golden and bubbly. Here's an overview of the ingredients needed to make it. The exact measurements are listed in the recipe card below:

Canned tuna: I use skipjack tuna in this recipe.
Mayonnaise: I like using avocado oil mayonnaise.
Mustard: I use Dijon musrad. It's creamier and less vinegary than yellow mustard.
Shredded Gruyere cheese: Other melty cheeses like cheddar or provolone will work too, but Gruyere is especially flavorful.
Chopped red onion: Make sure it's finely chopped.
To season: Salt, black pepper, and cayenne pepper. The cayenne pepper doesn't make the casserole very spicy, at least to my palate, but it does add a subtle kick.
Chopped parsley: I use it mostly for garnish, so you can skip it if you don't have it on hand. It does add a nice splash of color, though.

Variations

You can use tuna in olive oil instead of tuna in water. It's delicious!
Try using sour cream instead of mayonnaise. Both work, but personally, I prefer mayonnaise.
Dill makes a nice addition to this recipe. You can add a tablespoon of minced dill to the mixture.
Sharp cheddar or provolone are good substitutes for Gruyere. Smoked Gouda is also very good.

Instructions

Scroll down to the recipe card for detailed instructions. Here are the basic steps for making this recipe:

Simply mix all the ingredients together, reserving some of the cheese and the parsley.

Transfer the mixture to a small baking dish and sprinkle the top with the remaining cheese.

The mixture was transferred to the baking dish and topped with cheese.

Bake the casserole until heated through, about 15 minutes in a 400°F oven. Garnish with parsley and serve.

Expert Tip

You can bulk up this casserole by adding 2 cups of cooked riced cauliflower, increasing the mayonnaise to ½ cup, and dividing it into 3 servings.

Recipe FAQs

Why is my casserole dry?

This casserole can become dry if the ratio of tuna to creamy ingredients (mayonnaise and mustard) is too high.

I find that ⅓ cup of mayo works well, but depending on the brand of tuna you use, you might need to increase it and use up to ½ cup.

Can you make a tuna casserole without noodles?

Yes! I do it all the time. It's a different recipe than classic ones, and you'll want to serve it with something for scooping it out, such as fresh-cut veggies, keto crackers, or pork rinds. But it's very, very good.

Can you freeze this casserole?

Yes. Once completely cool, you can wrap the baking dish in plastic wrap followed by a layer of foil. Freeze it for up to three months, then thaw it in the fridge.

Reader Review

On Instagram, @shelikeshergreens posted this gorgeous photo of her casserole. She says, "I made my own mayonnaise for this casserole. I didn’t have gruyere so I used cheddar instead. I added dill to the mix to bring some freshness to it. This was amazing with the sautéed beans!"

A reader photo of a keto tuna casserole with a side of green beans.

Serving Suggestions

This casserole is rich and filling. As you can see in the recipe card below, a serving has 465 calories. So I simply serve it with fresh-cut veggies for scooping it out of the baking dish (or plate). It's also good with a side of microwave broccoli and with plain pork rinds.

Scooping the hot casserole with a pork rind.

Storing Leftovers

The leftovers keep well in the fridge for 3-4 days, or you can freeze them for up to three months if you want to keep them for longer. Gently reheat them in a 350°F oven or in the microwave (covered) at 50% power.