In medium saucepan, bring water to a boil, add grits, and cook until thickened, about 5 to 7 minutes. Spread grits into 2 (13 by 9 by 2-inch) baking pans. Let cool.

Preheat the oven to 350 degrees F.

In medium skillet, cook onion and bell pepper in olive oil, until tender. Set aside. In medium skillet, cook sausage until cooked through. Add onion and bell pepper and combine thoroughly. Add spaghetti sauce to sausage mixture. Over low heat, simmer for 15 minutes.

Cut grits horizontally into 2 (13 by 9-inch) rectangles. Place 1 rectangle in bottom of a 13 by 9-inch casserole dish; add 1/2 sausage mixture, then dollop 1/2 of sour cream over sausage mixture, top with 1/2 of mozzarella cheese. Repeat layers.

Cook for 40 to 45 minutes. Let stand for 10 minutes before serving.