In a medium saucepan, bring 4 cups of water to a boil. Stir in the grits and salt, reduce heat to low, and cook for about 20-25 minutes, stirring occasionally until thickened.
Once the grits are cooked, stir in the milk, butter, and cheddar cheese until creamy. Keep warm.
In a large skillet, heat olive oil over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant.
Add the shrimp and Cajun seasoning to the skillet. Cook for 3-4 minutes, stirring occasionally, until the shrimp are pink and cooked through.
Stir in the chopped green onions and cook for an additional minute.
To serve, spoon the creamy grits into bowls and top with the shrimp mixture. Garnish with fresh parsley.