Wild Salmon with Grilled Sweet Onion and Corn Relish

INGREDIENTS

• 1 large sweet onion, peeled and sliced 1/2 in. thick
• 2 shucked ears corn
• About 2 1/2 tbsp. olive oil, divided
• 1 cup halved small cherry tomatoes (quartered if larger)
• 1/4 cup slivered basil leaves, plus sprigs
• 2 tablespoons fresh lemon juice, plus lemon wedges
• About 1 tsp. kosher salt
• About 1/2 tsp. black pepper
• 4 pieces boned wild salmon fillet (6 to 8 oz. each and 1 to 1 1/4 in. thick), rinsed and patted dry