In a pan over medium heat, add oil. Saute onions until it turns lightly brown. Transfer to a mixing bowl and let it cool.
Combine all the burger patty ingredients and cooked onions. Mix everything together, preferably by hand. Let the patty marinate for 15 minutes. Meanwhile, you can start preparing the buns, cheese and vegetables.
Gently shape the mixture into burgers about 3/4 inches thick; shape it slightly wider than the buns.
In a pre-heated frying pan with oil, cook the burger for 6 to 8 minutes on each side depending on how you like them.
Tuck into warm buns and add your favorite toppings. I used sliced cucumbers, grated mozzarella and cheddar cheese and ketchup mayo with pickle relish for the sauce. Oh yum!
Notes
If you don't have worcestershire sauce, just add a little bit more salt.