Cook the noodles according to package directions.

While the noodles are cooking, brown the ground beef and chopped onion together in a skillet over medium heat.

Drain off any excess fat from the skillet.

In the skillet, combine the drained noodles, sliced celery, catsup, sliced mushrooms (including the liquid from the jar), stewed tomatoes, salt, and pepper.

Stir well to ensure all ingredients are evenly distributed.

Cover the skillet with a lid.

Reduce the heat to low and simmer for 30 to 45 minutes, or until the celery is tender and the flavors have melded together.

Serve hot.