Preheat oven to 425°F. Toss zucchini, bell peppers, and red onion with olive oil, cumin, chili powder, salt, and pepper on a large baking sheet.
Roast vegetables for 20-25 minutes, stirring halfway through, until tender and lightly charred at the edges. Remove from oven and set aside.
Heat a large skillet over medium heat and add a small pat of butter. Place one tortilla in the skillet and sprinkle with about 1/3 cup cheese.
Top with a generous portion of roasted vegetables, another 1/3 cup cheese, and a second tortilla. Cook for 2-3 minutes until golden brown, then carefully flip and cook another 2-3 minutes until cheese is melted and both sides are crispy.
Remove from skillet, cut into wedges, and repeat with remaining tortillas and filling. Serve immediately with salsa, guacamole, and sour cream.