Add the butter and olive oil to a saucepan set over medium heat. When the butter has melted, add the onion and cook until soft. Add the garlic and cook for another minute. Turn the heat to high and pour in the milk and water. Bring to a boil and slowly whisk in the grits. Turn the heat to medium-low and cook, stirring occasionally, for 15 to 20 minutes. When done, dump in the cheese and stir until it is melted. Season with salt and pepper and set aside.
Add the bacon to a large skillet set over medium-high heat. Cook until golden browned and crisp. Remove and drain on paper towels. Pour out all but 3 tablespoons of the oil.
Set the skillet back over medium-high heat and when nearly smoking, add the shrimp. Cook until pink, about 1 1/2 minutes per side.
Scoop some of the cheese grits into a bowl and top with the shrimp, chopped bacon, and scallions. Season to taste with salt and pepper.