Heat oil in 12-inch nonstick skillet or Dutch oven over medium-high heat until hot. Add squash, zucchini and onion; cook and stir 5 minutes or until vegetables are crisp-tender.
Add tomato and oregano; cook and stir 1 minute. Sprinkle with salt and pepper. Add taco sauce; cook and stir 30 seconds or until sauce begins to boil. Reduce heat to low; sprinkle with cheese. Cover; cook 2 minutes or just until cheese is melted. Garnish with cilantro.