Mix together the tomato, shrimp, cucumber, leek, dill, ginger, garlic, jalapeno pepper, lime juice, olive oil and season with salt and pepper. Set aside for one hour to marinate.
Preheat the grill to medium-high heat.
Season the Mahi filets with lemon pepper, pressing the spice firmly but gently into the fish. Brush the Mahi filets with a little melted butter.
Place the filets onto the grill and cook for 3 minutes per side, or until the fish is just cooked through and easily flakes. Squeeze the juice from the lemon and lime over your fish and brush them lightly with the butter. Remove from grill and serve immediately with chunky tomato and shrimp salsa.