Cook the onion in a pan with the butter and chile flakes on medium heat. Stir often and cook about 20 minutes until fully caramelized.
Drain the tofu. Place the tofu on its side and slice down the center the long way. Slice each half in half again so you are left with 4 thin rectangular tofu slices.
Place the sliced tofu on paper towels to dry.
Meanwhile, split the ground beef in half and form two burgers the same size as the tofu.
Place the tofu on a hot griddle or frying pan with some oil. Sprinkle sesame seeds onto each piece of tofu to emulate a burger bun and lightly press them in.
Flip the tofu to brown the other side.
Meanwhile, cook the burger to medium, adding the cheese after flipping.
Build the burger by placing the bottom bun, followed by a smear of hoisin, then the burger, then the onions, peanuts, cucumber, cilantro, sriracha, and the top bun. Serve!