Menu Hashing - Burger concept

I was recently asked to hash through some menu ideas for an upscale burger concept. I thought immediately, "Oh gawd, another damn burger concept." Burger concepts are a dime a dozen and their failures are even cheaper. But, I tend to think left of center and, although I was forced to conceptualize within a certain set of parameters, I have come up with a few interesting offerings. This is one of them. I have taken the cliché "Tuna Slider" (apparently a required California standard) and added my suggestion to the pile.

Seared Tuna Slider.

Ingredients:

• small (<15 lbs whole fish) yellowfin loin fabricated into medallions
• 4 medium green tomatoes
• 4 large white onions
• Pickling Liquid
• 4 cups white wine vinegar
• 2 cups white sugar
• 4 oz chopped cilantro
• FGT (fried green tomato) Dredge
• 1 cup AP flour
• 1/2 cup corn meal
• 2 tsp kosher salt
• 1/2 tsp ground white pepper
• 1/2 tsp onion powder
• 1/2 tsp garlic powder
• pinch cayenne pepper
• 2 large eggs
• 1 cup buttermilk
• 12 small Brioche Rolls (or store bought equivalent)
• good mayonnaise (kewpie is my guilty pleasure)
• Clarified or Unsalted butter (for cooking with)
• Oil for frying (at home, shallow fry is OK)
• S/P to taste (for searing the fish)

Start the pickled onions first. Slice the onions in rings, as thinly as possibly (I used a meat slicer to shave them). Mix the vinegar and sugar together until completely incorporated. Add the onions, add the cilantro, mix well. Set aside.
Mix the dredge ingredients well. Set aside.
Slice the green tomatoes. You should get approximately 3~4 usable slices per tomato. 
Mix buttermilk with eggs, add tomato slices. 
Remove tomato slice from buttermilk and place in dredge, coating completely. Re-dip tomato slice in buttermilk and re-dredge. Set aside. Fry tomato slices when all have been coated.
Brush hot grill with butter, sear tuna quickly. 
Brush cut rolls with butter and grill them until golden.
Assemble sandwich on grilled roll with tuna on bottom topped with fried green tomato and pickled white onions. Place a small amount of mayo on the inside of the top bun.