Combine cumin, smoked paprika, chili powder, garlic powder, onion powder, salt, and pepper in a small bowl. Pat chicken thighs dry with paper towels, drizzle with 1 tbsp olive oil, and press spice rub over every surface.
Optional: Rest the coated chicken at room temperature for 15 minutes or refrigerate for up to 8 hours.
Heat a cast iron or heavy stainless skillet over medium-high heat for 2 minutes. Add remaining 1 tbsp olive oil and let it shimmer. Place chicken smooth-side down in a single layer without crowding.
Cook without moving for 6 to 7 minutes until a dark crust forms and the chicken releases naturally. Flip and cook 5 to 6 more minutes until internal temperature reaches 74°C (165°F).
Transfer to a cutting board, rest for 5 minutes, then slice thinly across the grain. Drizzle with lime juice.
Warm corn tortillas in a dry skillet for 30 to 45 seconds per side. Wrap in a towel to keep soft.
Fill each tortilla with 2 to 3 tablespoons of chicken, shredded cabbage, avocado, salsa, and cilantro. Serve with lime wedges.