Cut the sirloin steak into bite-sized cubes and pat dry with paper towels.

In a mixing bowl, whisk together soy sauce, beef broth, Worcestershire sauce, garlic, onion powder, smoked paprika, and black pepper.

Pour the marinade over the steak cubes in the slow cooker and stir to coat evenly.

Cut the butter into small pieces and distribute over the steak and marinade mixture.

Cover the slow cooker and set it to cook on LOW for 4 to 5 hours or HIGH for 2 to 3 hours.

Garnish with fresh parsley before serving, hot over mashed potatoes, rice, or as an appetizer.