In a skillet, saute diced onions in oil until translucent.
Add ground meat to the skillet and cook on medium heat until well browned.
Season with salt and pepper.
Cut the Hawaiian rolls in half crosswise, leaving the individual buns intact.
Spread butter on the inside of the rolls and sprinkle with garlic powder.
Place on a prepared baking sheet and broil on low for 5 minutes, until the rolls turn golden brown.
In a small bowl, mix mayo, ketchup, and mustard.
Spread the mixture on both sides of the Hawaiian rolls.
Layer 4 slices of cheese on the inside of the buns, top with ground beef mixture, layer with the remaining 4 slices of cheese and place the tops of the buns on top.
Brush olive oil over the tops of the Hawaiian rolls and sprinkle with bagel seasoning.
Bake for 10-15 mins at 350 degrees F.