Bring 4 cups of water to a boil in a saucepan. Stir in the grits and reduce heat to low. Cook for 5-7 minutes, stirring occasionally, until thickened.
Remove from heat, stir in butter and cheddar cheese. Season with salt and pepper. Cover and keep warm.
Heat olive oil in a large skillet over medium-high heat. Add sliced sausage and cook until browned, about 4-5 minutes.
Add shrimp to the skillet along with Cajun seasoning and garlic powder. Cook until shrimp are pink and opaque, about 3-4 minutes.
Spoon cheesy grits into bowls, top with shrimp and sausage mixture.
Garnish with chopped parsley if desired and serve immediately.