Thaw fish, if frozen. Rinse fish; pat dry with paper towels. For tomato chutney, in a medium saucepan cook leek or green onions in 2 teaspoons hot oil over medium heat just until tender. Remove from heat. Stir in tomato, basil, capers, pepper, and salt. Set aside.
Brush remaining 2 teaspoons oil over fish. Place on the rack of the grill directly over medium heat. Grill for 4 to 6 minutes per 1/2-inch thickness of fish or until fish flakes easily when tested with a fork, turning once halfway through grilling. Serve with warm tomato chutney. Makes 4 servings.