In a bowl, combine olive oil, cumin, paprika, garlic powder, salt, and pepper. Add the fish fillets and coat them evenly. Let marinate for at least 10 minutes.
Preheat the grill to medium-high heat. Grill the fish for 4-5 minutes on each side until opaque and easily flaked with a fork.
In a separate bowl, mix the avocado, cherry tomatoes, red onion, lime juice, cilantro, and a pinch of salt to make the salsa.
Warm the tortillas in a pan over medium heat for about 30 seconds each side.
Assemble the tacos by adding a piece of grilled fish on a tortilla, topping with avocado salsa, shredded lettuce, and sliced jalapeños. Sprinkle with feta cheese if desired.
Notes
Try adding a squeeze of fresh lime juice to enhance flavors. For a spicier kick, add more jalapeño slices.