Put roast in your slow cooker. Sprinkle with garlic powder and onion powder, and season with salt and pepper. Pour BBQ sauce over meat.
Cook on Low for 6 to 8 hours.
Remove meat from slow cooker, shred, and return to slow cooker. Cook for 1 more hour.
For Polenta
In a large deep pan over high heat, bring water and salt to a boil; stir in the polenta.
Reduce heat and simmer gently, stirring frequently to avoid sticking, until mixture is very thick (about 30 minutes). Be sure to use a long-handled spoon to avoid burns from the popping and bubbling mixture!
Stir in the ghee and additional salt, if you prefer.
Spray a medium-sized bowl with canola oil spray. Spoon polenta into the bowl and let set for 10 minutes.
Invert onto a flat plate; mixture should continue to hold shape of the bowl.
Cut polenta into thick slices (like cake) and serve hot topped with the BBQ beef.