In a large cast iron skillet, heat the vegetable oil over medium high heat. Add the onion and poblano pepper and sauté for 4-5 minutes until the onion is translucent. Add the garlic and stir to combine.
Add the various bell peppers, zucchini and yellow squash and cook for another 5 minutes until the zucchini and squash are slightly soft. Stir in the corn and green chiles and continue to sauté for a few minutes more until the corn is warmed through. Remove the skillet from the heat and add the tomatoes, stir to combine.
Top the mixture with the grated cheddar cheese and cover for a few minutes to melt the cheese. Serve immediately.