Heat oven to 400°F for dark or nonstick pan (425°F for all other pans). Spray 15x10-inch pan with sides with cooking spray.
Unroll dough in pan; starting at center, press dough into 15x10-inch rectangle. Bake 4 to 6 minutes or until edges begin to set.
In small bowl, stir 6 tablespoons of the pesto with the garlic. Spread over crust. Sprinkle with cheese. Top with potato slices, and brush remaining 2 tablespoons pesto over potatoes.
Bake 8 to 10 minutes longer or until crust is golden brown and cheese is melted. Garnish with green onions. To serve, cut into 6 rows by 3 rows.