Sauté finely chopped onions on low flame (if you do this step too quickly by using a higher flame your onions will not become tender) with several tablespoons of oil until nicely browned and caramelized (soft but don't over brown).
In a large bowl mix together the remaining ingredients with the caramelized onions.
Cook the burgers on a medium flame in a frying pan or barbecue until nicely browned.
Top with lettuce, tomato, ketchup, sliced dill pickles, as you like. Enjoy!