Sprinkle a few mini pepperoni slices (or tiny pieces of regular pepperoni) on top of the cheese on each round, pressing them lightly into the cheese so they don’t slide off as it melts.
Return the tray to the oven and bake for another 6–8 minutes, or until the cheese is fully melted, bubbly, and starting to brown at the edges. For extra charred, pizza-parlor-style spots, switch the oven to broil for 1–2 additional minutes, watching closely so they don’t burn.
Let the zucchini bakes cool on the tray for 3–5 minutes; the cheese will set up a bit and make them easier to pick up. Serve warm straight from the foil-lined tray or transfer to a platter. They’re best eaten the day you make them, while the edges are still a little crispy and the cheese is gooey.
To keep it truly 4 ingredients, any tweaks should mostly be about swapping, not adding. For a different flavor, trade the pepperoni for cooked, crumbled breakfast sausage or finely chopped ham, keeping the same amount. You can also swap the mozzarella for another good melting cheese like provolone or Monterey Jack—just know mozzarella gives you the most classic, stretchy, kid-friendly vibe. If your kids (or you) like a little kick, choose a spicy pepperoni or use a sharp cheese for extra flavor without adding more ingredients. For a slightly firmer texture, slice the zucchini even thicker and bake them a minute or two longer in the first roast to dry them out more before adding cheese. These are best fresh, but you can meal prep by slicing the zucchini and shredding cheese the night before; store them separately in the fridge so you can assemble and bake in under 15 minutes on a busy day.