In a large skillet, heat the oil and butter over medium heat.
Add the onion and cook about two minutes.
Add the zucchini, tomato, corn salt & pepper. Mix all ingredients well.
Cover, reduce heat to low, and simmer for 8 minutes. Remove from heat and sprinkle the shredded cheese.
Replace the cover on the skillet and allow to sit until the cheese melts, 2 to 3 minutes.
Serve warm and sprinkle with some of queso fresco.
