In a large shallow bowl, combine lime juice, oil, garlic, cumin, salt, chili and cilantro; mix together. Add the chicken thighs and If time allows, let marinate for 30 minutes.

Heat a large skillet or pan (12-inch | 30cm) on medium-high heat until smoking. Add a drizzle of olive oil to lightly coat the bottom of the pan. Sear the chicken on both sides until golden, charred and cooked right through (about 8 minutes per side, depending on the thickness of your fillets). Flip them a couple of times while cooking so they get a nice even char.Transfer chicken to a warm plate, loosely tent with foil and let rest.

Add the peppers and onions to the skillet (drizzle with a little extra oil only if needed), and cook until the onion is soft and the peppers are slightly charred and cooked to your liking. Season with salt and pepper.

Slice chicken into strips.Serve with warmed tortillas, chopped cilantro and sliced avocado (plus your desired fillings).