Slice the zucchini into ¼-inch-thick slices. You can leave them unpeeled.
Preheat your broiler on high and position an oven rack 4 inches below the heating element (in most ovens, this is the top rack). Line a rimmed baking sheet with foil and spray it with olive oil.
Arrange the zucchini slices on the prepared baking sheet. Lightly spray them with olive oil and sprinkle them with salt, pepper, and garlic powder.
Broil the zucchini slices until tender and lightly browned, about 2 minutes per side. Keep a close eye on them! Some might brown faster than others – remove them to a plate and keep broiling the rest.
Remove the pan from the oven. Spoon a little marinara sauce on top of each zucchini slice. Top with cheese and (if desired) pepperoni.
Return the pan to the broiler just until the cheese is melted, for 30-60 more seconds. Serve immediately.
Video
Notes
Look for firm zucchini with smooth, dark green skins. Large zucchinis work better in this recipe.
The nutrition info includes pepperoni.
If you prefer baking to broiling, you will need to bake the zucchini in a very hot oven (450°F) for 5-10 minutes per side, depending on how hot your oven runs. Then top them with pizza toppings and return them to the hot oven just to melt the cheese - a matter of seconds.
You can keep the leftovers in an airtight container in the fridge for up to three days. Place them on paper towels to absorb extra moisture, and reheat them in the microwave at 50% power or in a 350°F oven.