Preheat the oven to 425°F. Toss the tortillas with 1 tablespoon of the oil and arrange on a large baking sheet. Bake until lightly brown and crispy, about 10 minutes. Heat the remaining 1⁄2 tablespoon oil in a large cast-iron skillet or sauté pan over medium heat. Add the onion and garlic and cook for 2 to 3 minutes, until the onion is translucent. Add the mushrooms and tomato and cook for 2 to 3 minutes, until softened. Season with salt and pepper. Turn the heat down to low and add the chiles and cheese, stirring constantly so the cheese melts uniformly. When the cheese has fully melted and starts to bubble, immediately remove from the heat and serve, using the tortilla chips to scoop directly from the pan.