Preheat your Dutch oven over medium-high heat and add the olive oil.
Season the chicken thighs with salt and pepper, then place them in the Dutch oven, skin-side down. Cook until the skin is golden and crispy, about 5-7 minutes, then flip and cook the other side for an additional 5 minutes. Remove the chicken and set aside.
In the same Dutch oven, add the diced onion and cook until translucent, about 3 minutes.
Add the sliced bell peppers and minced garlic, sautéing until the peppers are slightly softened, about 5 minutes.
Stir in the sliced mushrooms and cook for another 5 minutes, or until the mushrooms have released their moisture and started to brown.
Pour in the diced tomatoes, chicken broth, and red wine (if using). Stir in the dried oregano, dried basil, and red pepper flakes.
Return the chicken thighs to the Dutch oven, nestling them into the vegetable mixture.
Cover and simmer over low heat for 25-30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
Taste and adjust seasoning with additional salt and pepper if needed.
Garnish with fresh chopped parsley before serving.