Preheat your oven to 375°F (190°C). In a greased baking dish, layer the halved bagels.
Spread marinara sauce evenly over the bagels, making sure to cover them entirely.
Sprinkle a generous layer of shredded mozzarella cheese over the sauce.
Add sliced pepperoni, black olives, bell peppers, and mushrooms on top of the cheese.
Sprinkle dried oregano and garlic powder over the toppings for that classic pizza flavor.
Repeat the layering process with the remaining bagel halves, marinara, cheese, and toppings.