Adjust the cooking rack to the lowest placement and preheat toaster oven to 425°F on the BAKE setting.
While the oven preheats, quarter the zucchini lengthwise and then cut into 1/2-inch thick pieces. Cut the bell pepper and onion into 1-inch thick pieces.
Add the vegetables to a roasting pan. Drizzle with oil and sprinkle over the oregano, garlic powder, and salt and pepper, to taste. Toss to combine.
Roast vegetables for 10 minutes. Carefully remove the pan and stir. Return pan to oven and continue cooking until the vegetables have softened and started to brown, about 5 minutes more. Remove from the toaster oven and set aside.
Warm the Pitas:
Reduce the temperature to 375°F and warm the pitas by placing them directly on the cooking rack for 1 to 2 minutes.
Spread warm pitas with hummus. Layer with spinach, roasted vegetables, and crumbled feta.