In large nonstick skillet, combine onions, carrots and 1/3 cup water. Bring to a boil. Reduce heat; cover and simmer 4 to 6 minutes or until carrots are crisp-tender.
Add zucchini; cover and cook an additional 1 to 2 minutes or until zucchini is crisp-tender, stirring occasionally. Drain; stir in vinegar and lemon-pepper seasoning.