Preheat a large skillet over medium-high heat. Season the chicken thighs with salt and pepper to taste.

Add olive oil to the hot skillet and brown the chicken thighs on both sides until golden. Transfer them to the slow cooker.

Add the chopped onion and minced garlic to the same skillet and cook until softened and fragrant.

Add the sliced mushrooms, spinach, and bell pepper strips, and cook until golden.

Transfer the onion, garlic, mushroom, spinach, and bell pepper mixture to the crockpot with the chicken thighs.

Mix the chicken broth, heavy cream, and all-purpose flour in a small bowl until well combined. Pour this mixture over the chicken and vegetables in the crockpot.

Cover the crockpot and cook on low for 5 hours or until the chicken is tender and the sauce is thick and creamy.

Once done, adjust the seasoning with salt and pepper to taste. If desired, garnish with chopped fresh parsley before serving.