Cook orzo in salted water according to package directions; drain and rinse under cold water, transfer to a large bowl and combine with tomatoes and 1 tablespoon of the oil and garlic.
Meanwhile spray the onions, bell peppers and zucchini with olive oil; season with 1 teaspoon salt and black pepper, to taste.
Grill vegetables on a grill basket over oiled grates, covered, (or broil 4 inches from flame) 10-12 minutes or until lightly charred and tender, turning halfway.
Set aside on a cutting board to cool slightly, then dice into 1/2-inch pieces.
Toss with the remaining olive oil and vinegar and top with chopped basil.