Puree onion and food processor. Strain the puree through a mesh strainer, capturing the liquid in a bowl.
Mix remaining ingredients in a large bowl and add onion juice. Need throughly until mixture come tacky/sticky.
Using a 1/3 measuring cup, portion out your meat mixture. Then using wax paper, form the positions into patties with your hands make sure the patties are a little bit larger than the buns.