Brown the beef stew in a dutch oven with the olive oil; drain.
In the meantime, chop the vegetables.
Put the sweet potatoes and onion in the bottom of your slow cooker. Add the browned beef, then the celery, carrots, garlic, diced tomatoes, and 3 cups of the broth. Sprinkle the parsley, basil, salt, and pepper on top.
In a measuring glass, add the remaining 1 cup of beef broth and mix with the tapioca starch. Whisk until blended, then pour over the top of the stew.
Cook on high for about 4 hours or slow for 7-8 hours (depending on your slow cooker.)