Preheat oven to 450°.
Heat oil in a large nonstick skillet over medium-high heat. Add onion and garlic; sauté 1 minute. Add half of spinach; cook 1 minute or until spinach wilts. Add remaining spinach; cook 2 minutes, stirring constantly, until spinach wilts. Remove from heat; stir in feta and next 6 ingredients (through pepper).
Place dough on a baking sheet coated with cooking spray; pat dough into a 15 x 12-inch rectangle. Spread spinach mixture lengthwise over half of dough, leaving a 1-inch border. Fold other half of dough over filling; press edges together with a fork. Cut 5 (1-inch) diagonal slits in top of dough.
Combine milk and water; brush evenly over dough. Sprinkle with Parmesan. Bake at 450° for 15 minutes or until golden.