Combine first 4 ingredients in a large bowl, and stir well. Remove 1/2 cup lime juice mixture from bowl, and place in a blender; set remaining lime juice mixture aside. Add cilantro leaves to blender, and process until smooth; set the cilantro mixture aside.
Cut chiles in half lengthwise; discard seeds and membranes. Flatten chile halves with hand; set aside. Place zucchini halves, skin sides up, on a foil-lined baking sheet; broil 4 minutes. Turn zucchini over, and add chiles to pan, placing chiles skin sides up. Broil an additional 6 minutes or until chiles are blackened. Set zucchini aside. Place chiles in a heavy-duty zip-top plastic bag, and seal; let stand 15 minutes. Peel chiles. Cut chiles and zucchini into 1/2-inch pieces; set aside.
Drop cauliflower into a large Dutch oven of boiling water; cook 3 minutes. Add carrot, corn, and green beans; cook an additional 5 minutes or until crisp-tender. Drain well. Add cauliflower mixture, chile pieces, zucchini pieces, and onion rings to lime juice mixture in bowl; toss well.
Place scallops on broiler pan coated with cooking spray; sprinkle 1/4 teaspoon salt over scallops. Broil 4 minutes on each side or until done.
Spoon vegetables onto individual plates, and top with scallops. Drizzle cilantro mixture over scallops. Garnish with cilantro sprigs, if desired.