Preheat the oven to 375°F.

In a large skillet, heat olive oil over medium heat. Add the diced bell peppers, zucchini, and cherry tomatoes. Sauté for about 5 minutes until the vegetables are tender. Stir in the chopped spinach and cook for an additional 2 minutes until wilted. Remove from heat and let cool slightly.

In a mixing bowl, combine the sautéed vegetables with the shredded mozzarella cheese, Italian seasoning, garlic powder, salt, and pepper. Mix well to combine.

Using a sharp knife, create a pocket in each chicken breast by slicing horizontally, being careful not to cut all the way through.

Stuff each chicken breast with the vegetable and cheese mixture, dividing it evenly between the two breasts. Secure the openings with toothpicks if necessary.

Place the stuffed chicken breasts in a baking dish. Sprinkle the grated Parmesan cheese on top and drizzle with a little olive oil.

Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F.

Remove from the oven and let rest for 5 minutes before slicing.