Ina food processor, grind the oats to a coarse powder. Add the chickpeas, onion,flax, garlic, capers, oregano, salt and lemon and pulse to make a chunky mixture.
Form into four scant half cup patties, about 3/4 inch thick, and place on a plate,chill for an hour. Don't make them too thin or they will crumble in the pan.
Make Tzaziki by mashing the avocado and stirring in the remaining ingredients. Reserve.
In a large saute pan, drizzle avocado oil and heat over medium high heat. Place burgers in the hot pan and cook for about 2 minutes per side, until golden brown, turning and adjusting heat as needed.
Serve on toasted buns with Tzatziki, lettuce and tomato.