Heat oven to 400°F and line two sheet pans with parchment or a silicone mat.
Stir mozzarella, Parmesan, Italian seasoning, garlic powder, red pepper flakes, and black pepper in a bowl.
Scoop heaping tablespoon mounds onto the pans, spacing about 2 inches apart.
Flatten each mound slightly and press a few mini pepperoni pieces on top.
Bake until edges are deep golden and lacy, 7 to 9 minutes.
Cool on the pan 3 to 5 minutes, blot any excess oil, then transfer to a rack to crisp fully.
Serve warm or at room temperature.