Warm the sunflower oil in a large skillet over medium heat. Sauté the onions until they soften, about 3 minutes. Add the mushrooms and sauté until they start to soften, about 4 minutes. Add the zucchini and the chopped peppers and sauté until they begin to release liquid, about 3 minutes. Add the Old El Paso Low-Sodium Seasoning Mix and stir. Continue to cook until the mixture starts to simmer, about 3 to 4 more minutes. The zucchini may continue to release liquid while it cooks.
Serve with the cooked Old El Paso Vegetarian Refried Beans, Old El Paso Taco Shells, and the rest of the accompaniments.