Preheat oven to 425°F; toss zucchini, peppers, and onion with oil, cumin, chili powder, salt, and pepper on large baking sheet.
Roast 20-25 minutes until tender with lightly charred edges, stirring halfway; remove and set aside.
Heat large skillet over medium; add small butter pat. Add tortilla; sprinkle with about 1/3 cup cheese.
Top with generous vegetables, another 1/3 cup cheese, and second tortilla. Cook 2-3 minutes until golden brown; carefully flip and cook another 2-3 minutes until cheese melts and both sides crisp.
Remove; cut into wedges and repeat with remaining tortillas and filling. Serve immediately with salsa, guacamole, and sour cream.