Put all the patty ingredients in a large bowl, and mix well to combine - just don't overwork the meat too much.
Heat griddle or cast iron pan to medium high, add a little oil and put on the patties, cook until they're done to your liking - but be careful flipping them over as they're pretty soft.
While they cook, combine the mayo, mustard and chili sauce - mix and set aside.
Toast buns, and when patties are ready build with some sauce and lettuce & tomato.