Heat oven to 350°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In 2-quart saucepan, heat 2 1/2 cups water, 1 1/2 cups of the half-and-half, the butter and salt to boiling. Gradually stir in grits. Reduce heat to low. Cover; simmer 5 to 7 minutes, stirring occasionally. Remove from heat. Stir in 3/4 cup of the cheese until melted. Cool 15 minutes.
Stir 2 of the eggs into grits mixture. Pour into baking dish. Bake 20 minutes.
Meanwhile, in 10-inch skillet, cook bacon until crisp; drain on paper towels. Crumble bacon; set aside. Cook onion in bacon drippings over medium heat, stirring occasionally, until tender. In large bowl, beat remaining 8 eggs, the pepper and remaining 3/4 cup half-and-half with whisk; stir in remaining 1 1/4 cups cheese, the bacon, onion and spinach. Pour over crust.
Bake 25 to 30 minutes or until knife inserted in center comes out clean. Let stand 10 minutes before cutting.