Preheat the oven to 375°F (190°C).

In a medium bowl, combine the roasted red peppers, spinach, mozzarella cheese, minced garlic, Italian seasoning, olive oil, 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 roasted red pepper and spinach mixture, securing the opening with toothpicks if necessary.

If using breadcrumbs, sprinkle them evenly over the stuffed chicken breasts for added texture.

Place the stuffed chicken breasts in a greased baking dish and cover with aluminum foil.

Bake in the preheated oven for 25 minutes, then remove the foil and bake for an additional 10-15 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).

Remove from the oven, let rest for 5 minutes, and garnish with fresh parsley before serving.