Preheat the oven to 400°F (200°C).
Heat 2 tablespoons olive oil in a large oven-safe skillet over medium-high heat.
Add the finely chopped onion and cook 2–3 minutes until softened and edges are lightly golden.
Add the minced garlic and sauté 30 seconds until fragrant.
Pour in the crushed tomatoes (or marinara) and stir in the Italian seasoning, garlic powder, crushed red pepper, salt, and pepper; cook about 2 minutes to warm through.
Nestle the chicken breasts into the sauce and sear 1–2 minutes per side over medium-high heat just until lightly browned.
Transfer the skillet to the preheated oven and bake 10 minutes.
Carefully flip each chicken breast, top evenly with the mozzarella, and return to the oven; bake another 10 minutes or until the chicken reaches 165°F (74°C) internal temperature and the cheese is melted.
Garnish with fresh basil and serve immediately.
