Place one oven rack in upper third of oven, a second rack in lower third. Heat oven to 450 degrees F.
Halve each loaf lengthwise, then crosswise to make 8 pizza crusts.
Mix ricotta, pesto, Parmesan, salt, and pepper in bowl. Spread on crusts. Top with pepperoni, then mozzarella. Place 4 pizzas on one baking sheet, and 4 others on second sheet.
Bake one in upper third, other in lower third, of 450 degree F oven 10 minutes, until cheese melts. Cool 5 minutes.