1. Make the chicken: Preheat the oven to 425˚F (200˚C).
2.Pat the chicken thigh dry, then season with olive oil, salt, pepper, and cayenne. 3. In a cast-iron skillet over high heat, sear the chicken thigh, skin-side down, until the skin is crispy, about 10 minutes. Transfer the skillet to the oven and roast for 15 minutes, until the chicken is cooked through. Let cool slightly, then shred the meat. Leave the oven on.
4. Add the bell pepper, onion, and tomato to a medium pan over medium heat and sauté until the onion is translucent and the peppers and tomato are tender, about 6 minutes.
5. Meanwhile, heat the tortillas in olive oil or butter on the stove until warmed and slightly toasted. Set aside.
6. Divide the shredded chicken between the tortillas. Top with the sautéed vegetables, sliced avocado, and cheese. Place the tacos in the oven or on the stovetop over medium heat until cheese is melted, about 3 minutes.
7. Top with salsa, then serve.