Cook - Warm butter and oil in a large skillet over medium heat. Sauté onions until they become soft, 4-5 minutes. Add zucchini and squash and sauté until they soften slightly, another 3-4 minutes. Stir in corn and diced chiles and sauté for 5 minutes. Add tomatoes and sauté 5 minutes more. Transfer calabacitas to a serving bowl. Season with salt and pepper. Mix in cheese, cilantro, and serve.
2 tbsp Olive oil (Sub: vegetable oil), 2 tbsp Butter, 2 cups Sweet corn kernels, fresh, canned or frozen, 2 tsp Salt, 1 tsp Black pepper, 4 oz Canned diced green chiles, drained, 1 cup Queso fresco, crumbled (Sub: grated Monterey Jack, cheddar cheese, or rinsed feta cheese), Fresh chopped cilantro or parsley (optional garnish)