Season the chicken thighs with salt and pepper.

In a large skillet, heat the olive oil over medium-high heat. Brown the chicken thighs on both sides, about 4 minutes per side.

Place the sliced onion, bell pepper, and minced garlic at the bottom of the slow cooker.

Add the browned chicken thighs on top of the vegetables.

Pour in the crushed tomatoes and chicken broth.

Add the dried oregano, basil, thyme, and red pepper flakes (if using).

Stir to combine, then cover and cook on low for 6-7 hours or until the chicken is tender.

About 30 minutes before serving, stir in the sliced mushrooms.

Garnish with fresh parsley before serving.

For a different flavor, consider using boneless, skinless chicken breasts or adding a splash of red wine for richness. You can also throw in some olives or capers for a briny twist. If you prefer a thicker sauce, try stirring in a tablespoon of tomato paste along with the crushed tomatoes. As a lighter option, serve with quinoa or cauliflower rice instead of pasta or potatoes.