Mix ground beef, quick oats, onion, milk, eggs, 1/4 cup ketchup, parsley, garlic, salt, basil, and black pepper together in a large bowl until thoroughly combined; pat the mixture into a 9x5-inch loaf pan. Bake meatloaf in the preheated oven until firm and no longer pink inside, 1 to 1 1/4 hours.

The consensus seems to be either to just omit celery entirely or substitute with one of the following: fennel, parsley, parsnips, leeks, turnips, celeriac, bok choy (add at end of cooking!), chard or just more onion/carrot.