Brown the ground beef in a large skillet. Drain on a plate lined with paper towels, and wipe out the excess grease from the pan.
Preheat the oven to broil.
Add the olive oil, onion, bell pepper, zucchini, and a generous pinch of salt and pepper. Sauté for about 7-8 minutes or until the vegetables are soft and fragrant
Add the cooked ground beef and marinara sauce. Stir until everything is combined and spread evenly.
Sprinkle the cheese evenly over the top, followed by scattering the pepperoni out evenly.
Place into the oven and broil for 5-7 minutes or until the cheese is melted and bubbly and the pepperonis have crisped up slightly.