01 - Preheat oven to 400°F. Lightly grease a large baking dish with 1 tbsp of the olive oil.
02 - Arrange the sliced red, yellow, and green bell peppers along with the thinly sliced red onion evenly across the bottom of the prepared baking dish. Drizzle with the remaining olive oil, then 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. Lay the seasoned chicken breasts on top of the vegetable bed 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 bake for 20 minutes, allowing the chicken to cook gently in the steam alongside the vegetables.
06 - Remove the foil and sprinkle the shredded mozzarella and grated Parmesan cheeses generously over each chicken breast. Return the dish to the oven uncovered and bake for an additional 10 minutes, or until the chicken is cooked through to an internal temperature of 165°F and the cheese is melted, bubbly, and golden.
07 - Remove the dish from the oven and let the chicken rest for 5 minutes before serving to allow the juices to redistribute. Serve warm alongside the roasted peppers and onions.