Preheat the oven to 350 degrees F (175 degrees C).

In a large skillet over medium-high heat, cook the ground beef until evenly browned, stirring to crumble. Drain fat, and set aside.

Process the luncheon meat, cheese and onion in a food processor or run through a grinder until finely chopped. Transfer to a large bowl. Stir in the browned beef, tomato soup, tomato paste, garlic salt, and oregano until well blended. Spread a couple of spoonfuls of the meat mixture onto each bun half, and place them on a baking sheet.

Bake for 10 to 15 minutes in the preheated oven, until the meat is hot and the bun is crisp.