Marinate the Mahi Mahi: In a shallow dish, combine olive oil, lime juice, chili powder, paprika, cumin, garlic powder, onion powder, salt, and pepper. Whisk to blend. Add the mahi mahi fillets and coat evenly. Let marinate for at least 30 minutes, or up to 2 hours.
Prepare the Pineapple Salsa: In a bowl, combine chopped pineapple, red onion, cilantro, lime juice, jalapeño (if using), salt, and pepper. Stir well and set aside.
Heat the Pan: Heat a grill pan or cast iron skillet over medium-high heat. Brush with a little oil if needed.
Sear the Mahi Mahi: Remove the mahi mahi from the marinade and pat dry with paper towels. Sear the fillets for 2-3 minutes per side, or until cooked through and slightly golden brown.
Warm the Tortillas: Briefly warm the tortillas in a dry pan or microwave until pliable.
Assemble the Tacos: Using taco stands place a mahi mahi fillet in each tortilla. Top with pineapple salsa, avocado slices, and fresh cilantro. Squeeze lime juice over the tacos and enjoy!