Place the frozen meatballs and sliced mushrooms in the slow cooker.

In a bowl, combine Worcestershire sauce, powdered onion, powdered garlic, brown gravy mix, and water. Whisk until thoroughly blended.

Pour the sauce mixture over the meatballs and mushrooms in the slow cooker, stirring gently to coat evenly.

Cook on low for 4 to 6 hours or on high for 2 to 3 hours until the meatballs are fully cooked and the flavors meld.

After cooking, gently stir the mixture and adjust the seasoning with salt and pepper to taste.