Preheat your oven to 375°F (190°C).
In a skillet, heat the olive oil over medium heat. Add the minced garlic and sauté until fragrant, about 1 minute.
Add the chopped spinach to the skillet and cook until wilted, about 2-3 minutes. Remove from heat and let cool slightly.
In a mixing bowl, combine the sautéed spinach, roasted red peppers, and shredded mozzarella cheese. Season with Italian seasoning, salt, and pepper.
Prepare the chicken breasts by slicing them horizontally to create a pocket, being careful not to cut all the way through.
Stuff each chicken breast with the roasted red pepper and spinach mixture, securing the openings with toothpicks or tying them with kitchen twine.
Lightly spray a baking dish with cooking spray and place the stuffed chicken breasts inside.
Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (75°C).
Once cooked, remove from the oven and let rest for 5 minutes. Remove toothpicks or twine before serving.