Start the grits by adding water, half and half, salt, onion powder, garlic powder, and cayenne pepper to a medium saucepan. Bring the ingredients to a boil over medium-high heat. Slowly pour in the grits while stirring with a wooden spoon to avoid lumps.
Lower the heat to medium-low, cover the pot and cook the grits for 25 to 30 minutes, stirring occasionally.
Meanwhile, toss the shrimp with 1 tablespoon of blackened seasoning in a small mixing bowl and set them aside.
Heat the oil and butter in a 10-inch cast-iron or heavy-bottomed skillet over medium-high heat. Add the smoked sausage and cook for 3 to 5 minutes until browned. Add the bell peppers and onion and cook for 3 to 4 minutes until the vegetables soften. Add the garlic and cook for one additional minute until fragrant.
Season the veggies with 1 tablespoon of blackened seasoning and add the chicken stock, scraping up any browned bits from the bottom of the pan. Add the heavy cream and Worcestershire sauce and cook the sauce for 3 to 4 minutes until slightly thickened.
Add the shrimp and cook until the shrimp are opaque and the sauce has reduced a bit. This should take about 5 to 7 minutes. Be careful not to overcook the shrimp. Season the sauce with salt and cracked pepper to taste and remove the pan from the heat.
Once the grits are thick and creamy, remove them from the heat and stir in cheese and butter. Season the grits with more salt and cracked black pepper to taste.
Serve shrimp and grits immediately by spooning a couple of ladle-fulls of grits into a bowl and spooning the shrimp with sauce over top. Garnish with fresh chopped green onions and parsley and enjoy!