I love Burgers! Real burgers! And I really like Burgersteigwhich makes very good burgers close to U Schlesisches Tor. Like lots of burger places in Berlin (in German-speaking countries?), they chose a punny name based on how close Burger and Bürger (citizen) are. Bürgersteig means sidewalk.
So this tiny Burger place will always fresh grill your meat, you get a number when you order and will be called when it’s ready. The quality of the ingredients is top, the fries are crispy and not too greasy, the staff is very friendly and it’s pretty cheap. There isn’t a lot of space inside but there are a few tables outside for when the sun is shining, or you can enjoy your burger in one of the squares/parcs nearby.