Heat oil in heavy large nonstick skillet over medium-high heat. Add peppers and onion. Sauté until beginning to soften, about 4 minutes. Add zucchini and yellow squash and sauté until tender, about 8 minutes. Add vinegar to skillet and boil until liquid is reduced to glaze and coats vegetables, about 2 minutes. Season to taste with salt and pepper. Transfer to platter and serve.