Cut steak into bite-sized pieces (about 1 to 1½ inches). Season lightly with salt and pepper.
Place the steak bites in the slow cooker.
In a small bowl, add the water, onion soup, bouillon, and garlic powder. Stir to combine and pour over the steak.
Cover and cook on Low for 6–8 hours or High for 3–4 hours, until the steak is fork-tender.
If you’d like a thicker gravy, whisk together ⅓ cup cold water and 2 tablespoons cornstarch. Stir into the slow cooker during the last 15–20 minutes of cooking. Let it simmer with the lid slightly ajar until thickened.
Adjust the salt and pepper to taste. Spoon the steak bites and gravy over mashed potatoes, cooked rice, or egg noodles.
Notes
You can make this with sirloin steak, and it's delightful but more expensive. I tested this recipe with round steaks because they are much more economical (about half the price in my area) and are really well suited for long cooking time in the slow cooker. It really is a good option for making a round steak tender.
You can sear the meat up on the stove with a little oil in a hot pan before adding it to the slow cooker if you'd like.
Adjust the salt so that the meat and gravy are slightly salty so that when added to something plain like rice, potatoes, or noodles, it adds enough salt. You'll need to adjust it to taste based on what kind of bouillon you used.
You can omit the bouillon and use beef broth instead if that's what you have on hand.
You can thicken the sauce so it's a gravy, or you can leave it so it's more of an au jus; we like both!