Preheat oven to 400°F (200°C) and lightly grease a 9x13-inch baking dish with non-stick spray.
In a small bowl, combine the garlic powder, smoked paprika, onion powder, salt, and black pepper to create a dry rub.
Pat the chicken breasts dry with paper towels and rub them with 1 tablespoon of olive oil, then coat all sides evenly with the seasoning blend.
Place the seasoned chicken breasts in the center of the baking dish.
Toss the sliced bell peppers and onions with the remaining 1 tablespoon of olive oil and arrange them around and slightly over the chicken.
Bake in the preheated oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) as measured by a meat thermometer.
Remove the dish from the oven and sprinkle the shredded mozzarella cheese evenly over the chicken and vegetables.
Return the dish to the oven for an additional 3 to 5 minutes until the cheese is fully melted and starting to bubble.
Let the chicken rest for 5 minutes before serving to ensure the juices redistribute.