How to Make It
Stir together tomatoes, watermelon, red onion, chile, cilantro, mint, lime juice, 1 tablespoon canola oil, and 1/4 teaspoon salt in a medium bowl. Set aside.
Pat fish dry with paper towels. Cut 3 shallow slits into the skin side of each fillet. Sprinkle fillets with pepper and remaining 1/2 teaspoon salt. Heat remaining 2 tablespoons oil in a large stainless-steel or cast-iron skillet over high. Add fillets, skin side down, and cook until skin is browned and crisp, about 5 minutes. Turn fillets; cook until lightly browned and done, 1 to 2 minutes. Serve fish immediately, skin side up, topped with salsa.