In a bowl, whisk together olive oil, lemon juice, garlic powder, paprika, salt, and black pepper. Add the Mahi Mahi fillets to the bowl and coat them evenly with the marinade. Cover and let marinate in the refrigerator for at least 30 minutes.

Preheat the Grill

While the fish is marinating, preheat your grill to medium-high heat.

Grill the Mahi

Once the grill is hot, remove the Mahi from the marinade and place it on the grill. Cook for about 4-5 minutes on each side or until the fish flakes easily with a fork. Remove from the grill and let it rest for a few minutes.

Assemble the Sandwich

Prepare the Bread

Split the ciabatta rolls in half and lightly toast them on the grill or in a toaster until they are golden brown.

Layer the Ingredients

Spread tartar sauce on the bottom half of each ciabatta roll. Layer with lettuce leaves, grilled Mahi Mahi, tomato slices, red onion, and avocado slices.

Finish and Serve

Top with the other half of the ciabatta roll. If desired, sprinkle with capers. Cut the sandwich in half and serve immediately.