Bring 4 cups of water to a boil in a medium saucepan over medium-high heat. Add lima beans; cook 20 minutes or until tender. Drain. Add vinegar and oil, tossing well.
Bring 4 cups of water to a boil in a medium saucepan over medium-high heat. Add green beans and yellow wax beans; cook 7 minutes or until crisp-tender. Drain and combine lima beans, green beans, yellow wax beans, tomatoes, and basil in a large bowl. Sprinkle with 1/2 teaspoon salt and 1/4 teaspoon pepper; set aside.
Coat both sides of tuna with cooking spray; sprinkle with remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper. Place tuna on a grill rack coated with cooking spray; cook 2 minutes on each side or until desired degree of doneness. Cut each steak crosswise into 1/4-inch slices; arrange over bean mixture.
Wine note: The perfect wine for a summer salad needs to be refreshing and crisp, while at the same time capable of standing up to the "meatiness" of the grilled tuna and the acidity inherent in tomatoes. My favorite choice comes from France: Sancerre. (Sancerres are always made from sauvignon blanc grapes.) Try the Pascal Jolivet Sancerre 2003 (Loire Valley, France, $25), which is snappy, fresh, and full of citrus flavors. -Karen MacNeil