Since we are a low carb household (95% of the time 
), I have two distinct burger ādressingā preferences - with or without bun.
Without bun: Thick and medium rare max, cheese required. Usually a slice of Swiss or pepper jack paired with a slice of American, fully melted. I enjoy but do not require grilled or caramelized onions on this version (plopped on top). Mayo is a must - usually I add finely chopped green olives (olive burgers are childhood fave - local chain called Hot ānā Now served them), but if I donāt have any or am too lazy to chop them, I add a squirt of mustard, horseradish, hot sauce or pickled jalapeƱos to the mayo. Usually I leave the mayo on the side and dip, but sometimes I put it on top to let it mingle with the onions. If I donāt have mayo, blue cheese salad dressing is my preferred dipping alternative. Eat with fork. (BTW, I didnāt forget about my beloved bacon. Iāll eat it on/with a bunless burger, but itās hard to cut with a fork, so I usually donāt prepare them with bacon myself).
With bun: Thick and medium rare or thin/smash both fine, but I like a high meat-to-bun ratio, so with thin burgers I do a double. Cheese less important, but if itās there I want a strong one (stinky blue along with gruyere or similar). Martinās potato roll or something interesting/flavored (onion brioche, buttery rye toast, jalapeƱo cheddar roll, etc.). If the bun is just a regular bun, I donāt bother, and if itās a very thick bun I go open-faced. Bacon highly preferred and roasted cherry tomatoes are an acceptable topping (in addition to/combined with the toppings from my bunless assembly). Pickles and/or finely chopped raw onions also okay but I wouldnāt seek them out. I am flexible, though - the addition of mayo/dressing plus a tangy element is the only must. Everything goes on top of the burger so that the bottom bun can soak up burger juices (roasted tomatoes are the one exception - I usually put them on the bottom where they can mingle with the meat grease because they are also juicy).
Ketchup is a sin against humanity, and if I want lettuce or any other raw vegetable, Iāll order a salad (which I usually do instead of fries). Iām also okay with inventive meat-on-meat type toppings (like pulled pork or brisket, a slice of pork belly, bacon jam, etc) and deep fried things (onion straws, pickle chips, etc), but if the burger itself is really good I donāt need them. Not really a fan of chili on a burger (love it on a dog).
ETA: I forgot about mushrooms. I love a mushroom Swiss burger (preferably with bacon and onions) but have no interest in mushrooms in any other burger topping combination. Mushrooms should be well cooked and directly on top of the meat with the cheese on top so that it melts into them and secures them to the meat. I prefer this burger on a bun or rye toast.
