Place broccoli on rimmed sheet pan and drizzle with 1 tablespoon olive oil. Sprinkle with salt and pepper, toss with spatula so broccoli is coated with oil.
Place chicken on a cutting board and top with wax paper or plastic wrap. Using a meat mallet or a rolling pin, flatten chicken to about ½ inch — the key is that you want it to have even thickness.
Prepare three shallow bowls for breading the chicken. In the first, place flour, salt, pepper, garlic powder. Stir to combine. In the second bowl, beat the egg. In the third bowl, mix together panko bread crumbs, Parmesan cheese, and oregano.
Take one piece of chicken and coat in flour mixture, then dip in egg mixture. Let excess drip off and then dip in panko and Parmesan mixture. Place on baking sheet with broccoli. Repeat with remaining chicken breasts.
Bake for 15 minutes, toss broccoli around so it gets brown on all sides, and cook for 10 minutes more. Remove from oven and carefully add marinara sauce and mozzarella cheese to the top of each chicken breast. Return to oven for 5 minutes or until cheese is melted.
Notes
If you prefer, buy chicken cutlets and omit step 2.