Cut Wagyu into one-inch pieces. Combine all other ingredients and whisk until sugar and salt are dissolved. Pour over the beef and toss. Let marinate for 4 hours.
Grind meat through the large die of a meat grinder, and then pass through a medium die. Form into 1/2 pound patties and place in refrigerator until firm.
Cook burgers on the grill to desired doneness. Place a thick slice of Beecher’s Flagship Reserve cheese on the burger and let melt over the burger.
Grill the burger buns, then place a small handful of arugula on the bottom half of the bun. Next, place the burger on the bun and finish with a good amount of the pickled red onions.