Combine ground beef, ¼ cup Hellmann's® or Best Foods® Garlic Aioli and breadcrumbs in large bowl until well blended. Shape into 4 patties and set aside.
Heat olive oil in large nonstick skillet over medium-high heat and cook mushrooms and onions, stirring occasionally, until browned, about 5 minutes. Remove to bowl and stir in remaining 2 Tbsp. Aioli. Set aside.
Grill, broil or fry burgers to desired doneness. Place on toasted buns and evenly top with creamy garlic mushroom and onion mixture. Serve, if desired, with additional garlic aioli spread on buns.