Preheat the oven to 425°F. Line a rimmed baking sheet with foil, fit it with a wire rack, and spray the rack with oil.
Avocado oil spray
In a small bowl, mix the mayonnaise and Dijon mustard. Season the chicken breasts on both sides with salt and pepper. Brush them on all sides with the Dijon mixture.
1 tablespoon mayonnaise, 2 tablespoons Dijon mustard, 4 boneless skinless chicken breasts, ½ teaspoon Diamond Crystal kosher salt, ½ teaspoon black pepper
Dredge the chicken pieces in the almond meal, place them on the prepared wire rack, and spray their tops with oil.
1 cup almond meal
Bake the chicken uncovered until an instant-read thermometer inserted into the thickest part reads 165°F, 20-30 minutes (start checking after 20 minutes). The length of time you need to bake will depend on your oven and the size of the chicken pieces.
Top each chicken breast with two slices of ham (folded in two if necessary) and a slice of Swiss cheese.
8 slices ham, 4 slices Swiss cheese
Return the chicken to the hot oven for 2-3 minutes, just until the cheese melts. Garnish with chopped parsley. Allow the chicken to rest for 5 minutes before serving to allow the juices to redistribute and settle.
2 tablespoons parsley
Video
Notes
Seasonings, especially salt, are guidelines. Adjust to taste.
The sodium content will depend on the brand of ham you use.
It's best to use small chicken breasts. If yours are large (8 ounces or more), you'll need to bake them longer during the first baking stage before you top them with ham and cheese. If so, keep an eye on them. You might need to loosely cover them with foil to prevent the tops from burning. Check their internal temperature with an instant-read thermometer to ensure it has reached 165°F.
You can keep the leftovers in an airtight container in the fridge for 3-4 days. You can reheat them in the microwave, covered. However, I don't like reheated chicken, so I eat the leftovers cold with quick pickles on the side.