Using long-handled tongs, moisten a paper towel in cooking oil and lightly coat the grill rack. Brush tomatoes and onion rings with 2 tablespoons olive oil. Grill tomatoes over medium heat for 8-10 minutes or until skins blister, turning frequently; set aside to cool.
Meanwhile, grill onion rings over medium heat for 8-12 minutes or until charred, turning frequently.
Peel off and discard charred skin from tomatoes; coarsely chop tomatoes and onion.
In a large saucepan, saute garlic in remaining oil for 1 minute. Stir in the tomatoes, onion, beans, water and basil. Bring to a boil. Reduce heat; simmer, uncovered, for 10 minutes, stirring occasionally. Stir in the vinegar, salt and pepper.