Mix Tzatziki ingredients in a medium sized bowl and set in the fridge to keep cool.
Dice tomato and cut thin slices of the red onion and set aside.
Get your grill/pan/etc hot.
Mix meat ingredients together. Divide meat into 8oz (1/2 lb) portions (or you can use smaller 6oz portions). Flatten into patties that are about 1/2 inch larger than the buns.
Put a thumbprint in the middle of the patty so it doesn’t puff up when cooking.
Grill your burgers about 4min on the first side.
Flip burgers. Put the buns face down on the grill. Cook until you reach the correct temp (140F for medium), usually about 2 to 4 minutes.
Top burger with tzatziki, onions and tomatoes and enjoy!