Grecian Lamb Burgers W/ Tzatziki

First make the Tzatziki by combining the yougart, cucumber, dill, lemon juice, and salt & pepper in a bowl and mixing. Once mixed, cover and put in fridge until needed. This makes a thick tzatziki where you really see the ingredients. Just the way I like it.
Take the ground lamb (I buy leg of lab and cube it then run it through the food processor quickly so that it still has some chunks to it) and combine in a bowl with the oregano, thyme, salt and pepper. Make four equal-sized patties. Cut these patties into two and put a mound of feta cheese on the bottom patty and place the top patty over and reconnect by pinching around the edges. This will seal in the cheese which will cook into the patty.
Cook the patties and the sliced onions on the grill (or a grill pan for those stuck inside). Cook onions until they have great grill marks and begin to soften. Cook lamb patties to desired doneness but I would recommend not going past medium or you'll lose some of the lamb flavor. As patties finish remove to a cooler part of the grill and add the kefalotiri cheese to melt. Once melted let the lamb patties rest for a few minutes.
Quickly add the buns to the grill to toast up a bit. Just a few seconds is all thats needed on a hot grill.
Once the lamb has rested compose the burgers by adding the lamb to the bun and topping with the grilled onions, fresh greens, tomato and a dollop of the tzatziki.rnI like a cold beer if I'm having with fries or a cold moscolfiliero if I'm eating with salad.