Bring 4 cups of the water and 2 teaspoons of salt to a boil in a medium saucepan over high heat. Slowly whisk in the grits and bring to a boil. Reduce the heat to medium and continue cooking until the grits are soft and have lost their gritty texture, whisking every few minutes, 15 to 20 minutes. If the mixture becomes too thick, add remaining water and continue cooking until absorbed. Add the cheese and whisk until smooth; season with salt and pepper.
Place bacon in a medium pan over medium heat and cook until golden brown and crisp and the fat has rendered. Remove bacon with a slotted spoon to a plate lined with paper towels.
Remove all but 2 tablespoons of the bacon fat from the pan and place back on the heat. Add the olive oil and increase the heat to high Season the shrimp with salt and pepper, and add to the pan with the garlic. Saute until golden brown on both sides and just cooked through, 1 to 2 minutes per side. Remove shrimp to a plate. Reserve the garlic oil to drizzle over the finished dish.
Divide the grits among 4 bowls and top each with 5 shrimp. Drizzle the top with some of the bacon-garlic oil (that the shrimp were sauteed in) and sprinkle with some of the green onion.