Preparing this Easy One Pan Italian Chicken In Tomato Sauce is straightforward and enjoyable. Follow these steps to achieve delicious results:

1. Season Chicken: Start by seasoning the chicken thighs generously with salt and black pepper on all sides.
2. Heat Olive Oil: In a large skillet or frying pan, heat the olive oil over medium-high heat.
3. Brown Chicken: Add the chicken thighs, skin-side down, and cook for about 5 minutes or until they are golden brown. Flip them and brown the other side for another 5 minutes. Remove from the pan and set aside.
4. Sauté Onions and Garlic: In the same pan, add the chopped onion and sauté for about 3-4 minutes until translucent. Add the minced garlic and cook for an additional minute, stirring constantly to prevent burning.
5. Add Tomatoes and Spices: Pour in the crushed tomatoes, oregano, basil, and red pepper flakes if using. Stir well to combine.
6. Return Chicken to Pan: Carefully place the chicken thighs back into the skillet, skin-side up. Ensure they are nestled in the sauce.
7. Simmer: Reduce the heat to low, cover the pan, and simmer for approximately 25–30 minutes, until the chicken is cooked through and the juices run clear.
8. Add Spinach: In the last 5 minutes of cooking, add the fresh spinach to the pan, making sure it wilts into the sauce.
9. Cheese Topping: Just before serving, sprinkle the grated Parmesan cheese on top of the chicken and let it melt.
10. Finish and Serve: Once the cheese has melted, garnish with fresh basil leaves, and your dish is ready to serve!