Sprinkle the chicken with dry Ranch seasoning mix.
Top with shredded Parmesan and Mozzarella cheeses.
Bake uncovered for about 20 minutes.
Broil for the last 2-3 minutes (optional).
Remove from the oven.
Allow the chicken rest in the casserole dish. It will continue cooking as it rests for 5-10 minutes.
The chicken should be cooked through in about 20 minutes. The actual time depends on your oven. All ovens are different. It also depends on the thickness of your chicken breasts. Thin chicken breasts will cook faster.