Prep - Preheat oven to 375°F. Spray 8x8-inch glass baking dish with cooking spray; set aside. Cook spinach in microwave according to package directions.
Combine - Add cream cheese and garlic salt to spinach; stir until cheese melts and mixture is blended. Add undrained tomatoes, Monterey Jack cheese and onion; stir to combine.
Create - Place mixture in baking dish; bake 20 minutes or until hot and bubbly. Serve with pita chips or bread, if desired.