Heat oven to 375°F. In 6-cup popover pan or 6 regular-size muffin cups (2 3/4x1 1/4 inches), brush 1/2 teaspoon of the oil over bottom and side of each cup. Sprinkle 1/2 teaspoon of the flour over bottom and side of each cup.
Unroll dough sheet on cutting board. Sprinkle with garlic salt; spread with pesto. Top with pepperoni, arranging slices in 6 rows by 3 rows. Sprinkle with cheeses.
Using pizza cutter, cut dough in half lengthwise, then cut each half crosswise into thirds to make 6 equal pieces. Starting at short end, roll up each piece; place seam side down in popover cup so center of dough piece is on bottom and ends of dough are facing up (filling will show).
Bake 20 to 25 minutes or until tops are golden brown. Using knife or metal spatula, remove popovers from pan. Let cool 5 minutes before serving.