Add the cubed sirloin tip steak and potatoes to the slow cooker.
Arrange the sliced butter over the steak and potatoes.
Sprinkle the kosher salt, black pepper, garlic powder, onion powder, and steak seasoning evenly over everything.
Add the minced garlic.
Gently toss or stir so the steak and potatoes are evenly seasoned.
Cover and cook on LOW for 6–8 hours, until the steak is tender and the potatoes are cooked through.
Stir gently before serving so the steak and potatoes are coated in the buttery cooking juices.
Garnish with green onion if desired.
Serve hot.
