In the pot of the Ninja Foodi, set the Foodi to saute on medium-high heat. Add in the ground beef.
Add in the celery, onions, and green pepper.
Cook until the ground beef is browned and the veggies are soft.
Drain if needed and return to the pot.
Add in the water, ketchup, barbecue and tomato sauce, brown sugar, dry mustard, Worcestershire sauce, and apple cider vinegar.
Stir to combine.
Secure the pressure lid onto the Foodi, set the nozzle to "seal", cook on manual high pressure for 8 minutes.
Let this naturally release (do nothing) for 5 minutes.
After 5 minutes, move the nozzle to "vent", release all steam and remove the lid.
Stir the meat well adding in the 1/2 Tbsp of cornstarch and let sit for 2-3 minutes.
Add salt or pepper to taste and serve on buns.
Video
Notes
Regarding meat - It has been found that it's best to make this with 80%-85% ground beef, this will avoid any burning issues.Notes: To cook in the slow cooker, after draining the meat, add to the slow cooker and add remaining ingredients. Cover and cook on low for 2-3 hours until heated through. If you prefer to do this on the stovetop, after draining the beef, add the remaining ingredients and let simmer on low for 15-30 minutes.In all methods, the cornstarch is stirred in last if needed to thicken it up.