How to Make It
Place steaks in a single layer on a sheet of plastic wrap on a cutting board. Top with another sheet of plastic wrap. Using a meat mallet or small heavy skillet, pound steaks to 1/4-inch thickness. Discard plastic wrap. Sprinkle steaks evenly with 1/2 teaspoon each salt and pepper.
Preheat grill to high (450°F to 550°F). Combine tomatoes, vinegar, and remaining 1/2 teaspoon each salt and pepper in a large bowl.
Coat squash, zucchini, green onions, and eggplant with cooking spray. Place vegetables in a single layer on a grill grate coated with cooking spray. Grill squash and zucchini, uncovered, 2 minutes or until tender and grill marks appear. Grill green onions 2 minutes or until charred and slightly tender, turning occasionally. Grill eggplant 3 minutes on each side or until tender and grill marks appear. Coarsely chop green onions. Place eggplant, squash, zucchini, and chopped green onions in bowl with tomato mixture; toss to combine.
Place steaks in a single layer on grill grate coated with cooking spray; grill, uncovered, 2 minutes. Turn steaks; grill 1 minute or until desired degree of doneness. Place steaks on a cutting board; let stand 5 minutes. Thinly slice steaks against the grain.
Add mint and oil to vegetable mixture; toss to coat. Add basil; toss to coat. Divide vegetable mixture and steak slices evenly among 4 plates.