Preheat the oven to 375°F and brush a 9-inch springform pan with olive oil.
Unroll one refrigerated pizza crust and press it into the bottom and up the sides of the prepared pan.
Spread ½ cup marinara sauce evenly over the crust, then sprinkle 1 cup shredded mozzarella cheese on top.
Layer half of the sliced pepperoni, half of the diced green bell pepper, and half of the diced red onion over the cheese.
Place a second pizza crust on top of the first layer of toppings. Repeat the sauce, cheese, pepperoni, bell pepper, and onion layering.
Unroll the final pizza crust and place it on top. Spread the remaining ½ cup marinara sauce and sprinkle the last 1 cup mozzarella cheese over the top crust.
Bake for 30 to 35 minutes, until the crust is golden brown and the cheese is bubbly. Tent with foil if the top browns too quickly.
Let the pizza cake cool in the pan for 10 to 15 minutes before releasing the springform sides. Slice and serve warm.