In 10-inch nonstick skillet, heat oil over medium-high heat. Add onion, sugar and vinegar. Cook 8 to 12 minutes, stirring frequently, until onion is golden brown; stir in salt and garlic. Remove onion from skillet; set aside.
Heat oven to 400°F. Spray or grease 15x10-inch or larger dark or nonstick cookie sheet. Unroll dough on cookie sheet; starting at center, press dough into 15x10-inch rectangle.
Spoon onion mixture evenly over dough to within 1/2 inch of edges. Top with spinach; sprinkle with cheeses.
Bake 13 to 16 minutes or until crust is golden brown and cheese is melted.