1. Place the beef patty on the grill and cook well on both sides over medium heat.
2. Make sure to season it with salt and pepper to your taste.
3. On a hot griddle, drop the butter and saute the mushrooms in it. Add the vegetable oil too to facilitate the process.
4. Place the sauted mushrooms on the grilled patty.
5. Top with the sauted onions.
6. Place the cheese slice on top and let it melt down.
7. On one half of a split Kaiser roll, add the lettuce and tomato slice.
8. Top with a dressing of your choice.
9. Place the mushroom and melted cheese topped patty on the other half of the Kaiser roll.