Spicy Grilled Tuna (or other fish) with Heirloom Tomato Salsa - Rick Bayless

Ingredients

• 8 large garlic cloves, unpeeled
• Fresh hot green chiles to taste (roughly 2 serranos or 4 jalapenos), stemmed
• 1/3 cup fresh lime juice
• Salt
• 6 5- to 6-ounce fresh tuna steaks or skinless meaty fish fillets, such as snapper, grouper, wahoo, marlin or salmon, about 3/4-inch thick
• 1 small red onion, finely chopped
• Olive oil or vegetable oil for brushing or spraying the fish