Preheat your oven to 375 degrees F and spray a 9 x 13 inch baking dish with a non-stick spray. Set aside.
In a large pot, combine the chicken broth, whole milk and heavy cream. Bring it to a boil and then reduce the heat to low. Stir in the grits, cover and cook for 15-20 minutes until thick. Stir the grits occasionally.
While your grits are cooking, prepare your bacon and spinach mixture. In a large skillet, add the bacon. Cook over medium heat until crispy, about 8-10 minutes and then remove the bacon with a slotted spoon, leaving the bacon grease in the pan. Transfer the bacon to a plate that has been lined with a paper towel. With the pan left over medium heat, add the onion. Cook for 5-6 minutes or until tender and then stir in the spinach. Season with salt and black pepper. Cook until the spinach has wilted, about 3-4 minutes. Remove from heat.
When the grits have cooked through, stir in the butter, 3/4 cup of the mozzarella cheese, parmesan cheese and a dash of salt and black pepper. Stir until the cheese and butter have melted. Next, stir in the spinach mixture.
Pour the grits into the prepared baking dish. Sprinkle with the remaining 1/4 cup of mozzarella cheese. Bake until the cheese is melted and bubbly, about 10 minutes. Remove from heat and sprinkle with bacon.
Serve immediately and enjoy!