In a large skillet, heat the olive oil over medium heat. Once hot, add the finely chopped onion and sauté until translucent, about 3-4 minutes. Stir in the minced garlic and cook for an additional minute, until fragrant.
Pour in the crushed tomatoes or your chosen marinara sauce. Stir in the Italian seasoning, garlic powder, crushed red pepper, salt, and pepper. Let the sauce simmer for about 5 minutes, allowing the flavors to meld together.
While the sauce simmers, season the chicken breasts with salt and pepper. In a separate pan, heat a bit more olive oil over medium-high heat. Add the chicken breasts and cook for about 5-6 minutes on each side or until they are golden brown and cooked through.
Once the chicken is cooked, nestle it into the simmering sauce. Sprinkle the mozzarella evenly over the chicken. Cover the skillet and let it cook for an additional 3-4 minutes, or until the cheese is melted and bubbly.
Remove the skillet from the heat. Garnish with fresh basil leaves before serving.
