In a mixing bowl, combine chili powder, cumin, paprika, lime juice, and a pinch of salt. Add chicken thighs, ensuring they are evenly coated. Let rest for at least 15 minutes.

Heat a skillet over medium-high heat. Add oil if needed. Cook the marinated chicken thighs for about 7-10 minutes per side until golden brown and cooked through. Let rest for 5 minutes before slicing.

Prepare the pineapple salsa by mixing diced pineapple, chopped red onion, cilantro, and lime juice in a separate bowl. Toss gently to combine.

Warm the tortillas in the skillet for about 30 seconds on each side until pliable. Alternatively, microwave wrapped in a damp paper towel for 20-30 seconds.

Assemble the tacos with sliced chicken on each tortilla, topped with pineapple salsa, jalapeño slices, and avocado if desired.