Place duck breasts on a firm surface and, while pressing down gently on the top of each breast, slice each in half widthwise between your hand and the surface. Keep your fingertips up and away from the knife blade! When done slicing, you’ll have 12 slices. Combine kosher salt, pepper, Italian seasoning and onion powder and use mixture to season sliced duck on both sides. Stack seasoned meat together, wrap snugly with plastic wrap and refrigerate for 1 – 4 hours.
In a small saucepan over low heat, combine blue cheese, butter, beer and Tabasco. Stir constantly until mixture is smooth. Keep warm.
Coat onion slices with olive oil, salt and pepper. Place on a medium-hot, well-lubricated grill. Cook for 5 minutes. Place seasoned duck slices on grill and cook 2 – 3 minutes per side for medium-rare.
To assemble sandwich, arrange lettuce and tomato on the bottom of each bun. Top with 3 slices duck breast and grilled onions. Top with warm blue cheese sauce and other half of bun.