Sprinkle each chicken thigh with salt and pepper then dredge in flour.
Heat oil over medium-high heat in a large skillet and cook for about 4-5 minutes on each side or until chicken is golden-brown (it doesn't need to be completely cooked through).
Transfer chicken to a plate and set aside.
In the same skillet, saute peppers, onion, and garlic until onions become soft and transparent.
Reduce heat and slowly add marinara/spaghetti sauce to the skillet.
Add chicken back to the skillet and bring sauce to a simmer over medium-low heat.
Simmer for about 25 minutes or until chicken thighs are cooked through.
Before serving, top with mozzarella (optional) and fresh basil.
Can be served with pasta, steamed vegetables, or roasted potatoes.