MIX dressing and lemon juice. Toss mushrooms, zucchini, red peppers and onions in large bowl. Add dressing mixture; mix lightly. Place in foil-lined 15x10x1-inch baking pan.
BAKE at 400°F for 15 minutes, stirring after 10 minutes.
COVER tortillas with lettuce; top with vegetable mixture. Sprinkle with cheese. Roll up.