Brown the ground beef in a large skillet. Once the meat is almost completely browned add the onion to the skillet and continue cooking until the ground beef is cooked completely and the onion is translucent.
Drain the ground beef and onion well in a colander.
Add the drained ground beef and onion to a 6 quart crock pot slow cooker.
Add the cubed Velveeta cheese and salsa to the slow cooker.
Cover and cook on low for 2 hours. Occasionally stirring to keep the cheese from scorching.
Once the Velveeta cheese is melted and the ingredients heated through turn the slow cooker off and serve on fresh kaiser buns.