Heat oven to 375°F. Spray foil tart pans with nonstick cooking spray; place pans on large cookie sheet. Brown ground beef in 10-inch skillet until thoroughly cooked, stirring frequently. Drain.
Meanwhile, arrange 3 pepperoni slices in bottom of each sprayed tart pan. Sprinkle 1/4 cup of the cheese in each. Separate dough into 8 biscuits. Press or roll each to form 6-inch round.
Stir pizza sauce and mushrooms into ground beef. Divide beef mixture evenly into tart pans. Place 1 biscuit round over top of each, allowing dough to drape over edges.
Bake at 375°F. for 12 to 18 minutes or until deep golden brown. Cool 5 minutes. To serve, turn pizzas upside down onto individual serving plates. Lift off pans with fork, allowing pizza toppings to flow onto crusts. If necessary, scrape out any remaining cheese from pans.