Line the flounder filets in a large dish. Season with salt and pepper. Sprinkle the jalapeño, garlic, cumin and lime zest evenly over the fish. Drizzle 2 tablespoons of olive oil over the top and sprinkle with the juice from a quarter lime. Let sit 10 minutes.
Place the fish in an oiled fish basket and grill over medium-high heat until just cooked through; it will only take a couple of minutes on each side.
To serve, transfer the fish to a platter with a few sprigs of cilantro. Serve the fish flaked into warm corn tortillas with the toppings of your choice.