In a large skillet or Dutch oven, heat the olive oil over medium-high heat. Add the chicken thighs and drumsticks, skin-side down, and sear until golden brown, about 5-7 minutes per side. Remove the chicken and set aside.
In the same skillet, add the chopped onion and bell pepper. Sauté for about 5 minutes until softened. Add the minced garlic and cook for an additional minute until fragrant.
Stir in the diced tomatoes (with their juice), chicken broth, oregano, basil, red pepper flakes (if using), and season with salt and pepper. Bring the mixture to a simmer.
Return the chicken to the skillet, skin-side up. Cover and reduce the heat to low. Let it simmer for about 30-35 minutes, or until the chicken is cooked through and tender.
Once cooked, remove the chicken from the skillet and let it rest for a few minutes. Meanwhile, increase the heat to medium-high and let the sauce simmer uncovered for about 5-10 minutes to thicken slightly.
Serve the chicken over cooked pasta or with crusty bread, spooning the sauce over the top. Garnish with fresh parsley.