01 - Preheat oven to 400°F. Lightly coat a large baking dish with 1 tablespoon of the olive oil, spreading it evenly across the bottom and sides.
02 - Arrange the sliced red, yellow, and green bell peppers along with the red onion in an even layer across the bottom of the prepared baking dish. Drizzle with the remaining 1 tablespoon of olive oil and sprinkle with half of the salt, black pepper, Italian seasoning, and smoked paprika. Toss gently to coat all vegetables evenly.
03 - Pat the chicken breasts dry with paper towels. Season both sides of each breast with the remaining salt, black pepper, Italian seasoning, and smoked paprika, pressing the spices gently into the meat. Lay the seasoned chicken breasts on top of the bed of vegetables in the baking dish.
04 - Scatter the minced garlic evenly over the chicken breasts and surrounding vegetables.
05 - Cover the baking dish tightly with aluminum foil and place in the center of the oven. Bake for 20 minutes to allow the chicken and vegetables to cook through in the trapped steam.
06 - Carefully remove the foil and sprinkle the shredded mozzarella and grated Parmesan cheeses evenly over each chicken breast. Return the dish to the oven uncovered and bake for an additional 10 minutes, or until the chicken registers 165°F internally and the cheese is fully melted with golden-brown spots on top.
07 - Remove the baking dish from the oven and let the chicken rest for 5 minutes before serving. This allows the juices to redistribute throughout the meat. Serve each chicken breast over a portion of the roasted peppers and onions.