This delicious keto tuna casserole has no noodles, but it has plenty of flavor! Ready in 30 minutes and made with simple everyday ingredients, it's perfect for a weeknight dinner.
Canned tuna is tasty, filling, and affordable. I always have it on hand, making it the natural choice when the fridge is bare. I use it to make tuna patties and tuna salad. I also use it in this keto tuna casserole, a delicious, filling, and well-seasoned mixture of canned tuna, chopped red onion, mayonnaise, and cheese, baked until golden and bubbly.
Ingredients and Substitutions
See the recipe card for exact measurements. Here are my comments on some of the ingredients.
- Canned tuna: I use skipjack tuna canned in water. You can use tuna in olive oil if you wish.
- 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. You can also add a tablespoon of minced fresh dill.
- 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.
Instructions
The detailed instructions and step-by-step photos are included in the recipe card. Here's a quick overview.
Simply mix all the ingredients together, reserving some of the cheese and parsley.
Transfer the mixture to a small baking dish and sprinkle the top with the remaining cheese.
Bake the casserole until heated through, about 15 minutes in a 400°F oven. Garnish with parsley and serve.
Reader Review
On Instagram, @shelikeshergreens posted this gorgeous photo of her casserole, which she graciously allowed me to share here. She says, "I didn't have gruyere, so I used cheddar. I added dill to the mix to bring some freshness to it. This was amazing!"
Recipe 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
This casserole can become dry if the ratio of tuna to creamy ingredients (mayonnaise and mustard) is too high. I usually find that ⅓ cup of mayo works well, but depending on the brand of tuna you use, you might need to increase it to ½ cup.
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.
You can keep the leftovers in an airtight container in the fridge for up to 4 days. Reheat them in a 350°F oven or in the microwave.
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.
Serving Suggestions
This casserole is rich and filling. 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/or with plain pork rinds, as shown in the photo below.
Recipe Card
Keto Tuna Casserole
Video
Ingredients
- 2 5-ounce cans tuna in water - drained and flaked
- ⅓ cup mayonnaise
- 1 tablespoon Dijon mustard
- ½ cup Gruyere cheese - shredded, divided
- ¼ cup red onion - minced
- ¼ teaspoon sea salt
- ¼ teaspoon black pepper
- ¼ teaspoon cayenne pepper
- ¼ cup parsley - chopped, for garnish
Instructions
- Preheat the oven to 400°F.
- In a medium bowl, mix together the tuna, mayonnaise, mustard, ¼ cup of cheese, onion, salt, pepper, and cayenne.
- Transfer the mixture to a small, 1-quart casserole dish. Sprinkle the remaining ¼ cup of shredded cheese on top.
- Bake the casserole until hot, for about 15 minutes. Remove it from the oven and sprinkle it with parsley for garnish.
- Serve immediately, with cut-up veggies and/or pork rinds for scooping out.
Notes
- You can bulk this casserole up by adding 2 cups of cooked riced cauliflower, increasing the mayonnaise to ½ cup, and dividing it into three servings.
- You can use tuna in olive oil instead of tuna in water.
- You can keep the leftovers in an airtight container in the fridge for up to 4 days. Reheat them in a 350°F oven or in the microwave.
- To freeze the casserole for later: 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.
Nutrition per Serving
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Disclaimers
Most recipes are low-carb and gluten-free, but some are not. Recommended and linked products are not guaranteed to be gluten-free. Nutrition info is approximate. Please verify it independently. The carb count excludes non-nutritive sweeteners. Please read these Terms of Use before using any of my recipes.
Pamela Hamel says
Love this Tuna Casserole, have made it many times.
Vered DeLeeuw says
Hi Pamela,
Thank you so much for making so many of my recipes and reviewing them! ❤️