In another bowl, whisk together the water, egg whites, and vinegar.
Pour the liquids into the bread mix and stir well to combine. Knead for about a minute, then allow to rest for a few minutes.
Line a baking sheet with parchment paper.
Split the dough into 6 equal parts. Form a 4 inch disk with each piece of dough and place them evenly on the baking sheet. Top each one with some sesame seeds and press them into the dough to help them stick.
Bake for about 40 minutes until cooked through.
Remove from oven, allow to cool, and slice in half.
Add a little olive oil to a frying pan over medium heat. Cook the onions for about 45 minutes until deeply caramelized.
Split the meat into 6 equal parts and form the burgers the same size as the buns. Season heavily with salt and pepper.
Cook the burgers in a large frying pan over high heat, or on a grill, to desired doneness.
Build the burgers starting with the caramelized onions on the bottom bun, then the burger, then the tomato, lettuce, pickles, and any other desired toppings or condiments. Serve.