Sear the ChickenIn a large skillet or Dutch oven, heat olive oil over medium-high heat. Season chicken thighs with salt and pepper. Add them to the skillet and sear both sides until golden brown. Remove chicken and set aside.
Cook the VegetablesIn the same pan, add chopped onion and sliced bell pepper. Sauté until soft and aromatic, about 4–5 minutes. Add garlic and cook for 1 minute more.
Deglaze and Build the SaucePour in the red wine, scraping the bottom of the pan to lift up any browned bits. Let simmer for 2–3 minutes to cook off the alcohol. Stir in crushed tomatoes, mushrooms, and Italian seasoning. Bring to a simmer.
Simmer the ChickenReturn the seared chicken to the skillet, nestling it into the sauce. Reduce heat and simmer for about 10 minutes, or until the chicken is fully cooked and tender.
Finish and ServeStir in the olives and adjust seasoning as needed. Serve warm over cauliflower rice, roasted veggies, or your favorite low-carb pasta alternative.