Prep the chicken and vegetables: pat the sliced chicken thighs dry with paper towel and season with 3/4 tsp kosher salt, 1/4 tsp black pepper and the 1 tbsp fajita seasoning. Drying the meat and seasoning it now promotes better browning (Maillard reaction) when it hits the hot pan — that caramelized crust is where a lot of the flavor comes from.

Make the quick guacamole: in a medium bowl halve and pit the avocados, scoop the flesh and mash lightly with a fork so it’s creamy but still slightly chunky. Stir in the juice of the lime, 2 tbsp chopped cilantro, 1/2 tsp salt and a pinch of pepper. Taste and adjust acidity or salt. Making the guacamole first keeps it fresh and lets the lime prevent browning while you cook the rest.

Warm the tortillas: stack the 8 corn tortillas and wrap them tightly in foil. Slide them into a 250°F (120°C) oven while you cook, or hold them in a covered dish on the counter. Warming keeps them pliable and allows you to char them briefly at the end without cracking — a warm tortilla folds and holds fillings better.

Heat a large heavy skillet (cast iron is ideal) over medium-high heat until very hot, then add 1 tsp neutral oil or 1/2 tbsp olive oil. Add the chicken in a single layer (work in two batches if needed — overcrowding steams instead of sears). Sear without moving for 2–3 minutes until well browned, flip and cook 2 more minutes until just cooked through (internal temp 165°F/74°C). High heat searing builds flavor quickly; finishing at a lower temp prevents dryness.

Remove the chicken to a plate and tent with foil to rest. Resting lets juices redistribute so the meat stays juicy; if you slice immediately you lose those juices onto the cutting board.

Using the same hot pan, add the remaining 1 tbsp olive oil. Add the sliced peppers and onion with a pinch of salt and the 2 minced garlic cloves. Cook over medium-high heat, stirring occasionally, until the vegetables soften and develop dark brown edges, about 6–8 minutes. Browning the vegetables intensifies their natural sweetness and complements the seared chicken. If the pan gets too dry, splash in a tablespoon of water to deglaze and lift browned bits.

Return the chicken to the pan, add any accumulated juices, sprinkle the optional 1/4 tsp ground cumin if using, and toss everything together for 1 minute to marry the flavors and reheat the meat. The final toss lets the seasoning coat the vegetables and the chicken absorb those pan flavors.

Char the tortillas (optional but restaurant-style): heat a second dry skillet or griddle over medium-high heat. Working in batches, place each warmed tortilla directly on the hot surface for 20–30 seconds per side until it develops brown spots and floppy edges. Charred spots add smokiness and texture; keep them warm folded in a tea towel or wrapped in foil.

To assemble: place 2 warm corn tortillas on each plate. Divide the chicken and pepper mixture into 4 portions and spoon onto tortillas. Add a spoonful of guacamole and 2 tbsp of salsa per person, finish with a sprinkle of chopped cilantro and an extra squeeze of lime if desired. Serving immediately while hot ensures the contrast between warm filling and cool guacamole.

Leftovers and storage: store chicken and peppers in an airtight container in the refrigerator for up to 3 days. Keep guacamole separate (press plastic directly on surface to limit browning) and warm tortillas briefly before serving.