In a skillet, melt 2 tablespoons of butter.
Cut smoked sausage into slices then saute in butter for approx 7 minutes on medium heat stirring occasionally to prevent sticking.
Remove sausage from skillet and set aside.
Add chopped cabbage, onion, and 1 tablespoon butter to skillet. Stir until butter is melted. Cover with a lid and allow to simmer on medium/low for approx 10 minutes.
Remove lid and stir adding 1/3 cup of water. Cover and cook on low/medium heat for 10 minutes.
Remove lid then and stir the cabbage from the bottom then add the remaining 1/3 cup water and cook for an additional 5 minutes if needed. (Depending on the size of your head of lettuce and how finely you chopped you may need to cook more or less)
Add the sausage back to the skillet along with 1/3 cup sugar-free BBQ sauce and cook on low/medium heat uncovered for 5 minutes.