Brown roast on all sides in oil in skillet. Transfer to slow cooker.
Add water to skillet to loosen browned bits. Pour over roast.
Sprinkle with seasoned salt, soy sauce, Worcestershire sauce, and garlic powder.
Top with apple and onion.
Cover. Cook on Low 5–6 hours.
Remove roast and onion. Discard apple. Let stand 15 minutes.
To make gravy, pour juices from roast into saucepan and simmer until reduced to 2cups. Combine cornstarch and water until smooth in small bowl. Stir into beef broth. Bring to boil. Cook and stir for 2 minutes until thickened.