Grilled Flank Steak Tostada

Name: Grilled Flank Steak Tostada
Ingredients: 3 Vidalia or other sweet onions, peeled; 1 jalapeno pepper, seeded and diced; 1 large clove garlic; 2 cups fresh cilantro leaves; 1 tablespoon olive oil; 3/4 tablespoon salt; 1 1/4 pounds flank steak, trimmed of excess fat; 4 small zucchini, cut lengthwise into 1/2-inch wedges; 8 eight-inch flour tortillas; 2 heads romaine lettuce, washed and cut into 1/8-inch-wide slices; 6 tomatoes, cut into 1/4-inch-thick rounds; 4 radishes, sliced into paper-thin rounds; 4 limes, halved; Olive-oil cooking spray