Preheat oven to 425 degrees. In a large skillet, saute the spinach until wilted, about 6-8 minutes. Drain spinach in a colander and squeeze with some paper towels to remove water; set aside.
Using same skillet, heat oil over medium. Add onion and garlic and saute until lightly browned, 5 to 8 minutes.
Add the milk and warm it over high heat; whisk in the cream cheese and stir til combined. arm milk over high heat. Add Worcestershire sauce and hot sauce and stir to combine.
Combine the mozzarella and Parmesan cheeses. Add one cup to the mixture in the skillet and stir until combined.
Add the spinach and water chestnuts and mix thoroughly. Season with salt and pepper
Put the mixture into a lightly oiled and shallow 1.5 quart dish (I used two smaller ramekins) and top with the remaining cheese.
Bake until bubbly and golden brown, 20 to 25 minutes. Serve hot with crackers or toasted baguette slices.