Pat shrimp dry and place in a large mixing bowl. Sprinkle cajun seasoning on top and toss to coat. Set aside.

In a large skillet over medium-high heat, cook bacon until almost cooked. Add onion and cook 2 minutes, stirring frequently. Add garlic and cook just until fragrant, about 30 seconds. Add shrimp and cook for about 1 minutes on each side, until no longer pink and slightly golden. Add butter and toss to coat. Remove from heat, cover, and keep warm while you prepare the grits.

Bring milk, water, and salt to a boil over medium-high heat. Reduce to a simmer and add grits. Cook until thick, stirring frequently, about 5 minutes. Remove from heat and stir in cheese until melted.

Serve the shrimp mixture on top of the grits with green onions on top.