In a mixing bowl, blend the bell peppers, jalapeños, garlic, olive oil, lemon juice, paprika, cumin, salt, and pepper until smooth. Set aside half of the marinade for later to use as a sauce.

Place the chicken thighs in a large zip-top bag or bowl, and pour the remaining marinade over them. Seal the bag or cover the bowl, ensuring the chicken is well-coated. Marinate for at least 30 minutes or overnight for best flavor.

Preheat your grill to medium-high (around 400°F) or the oven to the same temperature.

For grilling, remove the chicken from the marinade and grill skin-side down for 10–12 minutes, flipping halfway, until the internal temperature reaches 165°F. For baking, arrange on a baking sheet and bake for about 25 minutes.

In a small saucepan, bring the reserved marinade and chicken stock to a simmer over medium heat. Cook for 5-7 minutes until slightly thickened. Stir in butter if desired.

Let the chicken rest for 5 minutes before slicing. Drizzle the sauce over the chicken and serve alongside your favorite sides.