Special equipment: a 6-inch cast-iron skillet
Preheat the oven to 375 degrees F. Lightly grease a 6-inch cast-iron skillet with canola oil spray.
Remove the biscuits from the package and lay them out on a clean work surface. Gently pull the layers apart at the middle to divide the biscuits in half. Gently pull each of the halves apart so you are left with four thin, round biscuits each (32 in all). Don't worry if any biscuits tear: just press the torn pieces back together.
Place 1 teaspoon of the mozzarella in the center of each biscuit round; you will use about 1 1/2 cups of the mozzarella for this. Fold the dough around the cheese and roll into balls. Arrange the balls in a circle around the edge of the prepared skillet, then work your way in until you have completely filled the cast-iron pan with the dough balls. If you start to run out of room as you get closer to the center of the skillet, gently push the dough from the center towards the edges of the pan to make more space.
Melt the butter in a medium skillet over medium-high heat. Once melted, stir in the scallions, garlic, red pepper and salt. Cook until the butter is just beginning to brown and the garlic is lightly toasted and very fragrant, 2 to 3 minutes. Remove the pan from the heat and stir in the vinegar. Pour the melted butter evenly over the top of the dough and sprinkle with the remaining 1/2 cup mozzarella.
Bake until the dough is cooked through and golden brown, 25 to 30 minutes. Remove from oven and let cool slightly, about 10 minutes. Serve in the skillet.