Heat oil in large nonstick skillet over medium heat until hot. Add zucchini, onion, corn and salt; cook 4 to 5 minutes or just until vegetables are crisp-tender.
Place 3 tortillas on work surface. Divide vegetable mixture evenly onto tortillas, spreading to within 1/2 inch of edges. Top with chiles; sprinkle with cheese. Top with remaining tortillas.
In same large nonstick skillet, cook each quesadilla over medium heat for 2 minutes. Carefully turn quesadilla; cook an additional 2 to 3 minutes. Cut each quesadilla into eight wedges. Serve with salsa.