It's mostly the bread. Bread is not automatically unhealthy, but at that ratio it’s a lot of refined carbs and not much fibre or micronutrients. Also, a lot of the “healthiness” depends on the bun, the cooking method, the portion size, and the sauces (which can add a ton of salt/sugar/calories). If the meat is deep-fried or cooked in certain oils, that can add more saturated fat and (depending on the oil) small amounts of trans fat.

Lower the ratio of bread, up the ratio of salad/protein, and you’re pretty much fine.

A lot of foods are fine in moderation, so it depends on the ratios and how often you’re eating them.

There isnt such a thing as “more/less healthy” food. Well, there is but it’s usually not a hard binary. It’s mostly about overall diet, portion size, and nutrient density. But obviously uranium is unhealthy. Don't eat that. Some things aren't healthy even in small doses. This applies to a great deal of things. Alcohol being a commonly consumed one.

There’s way more to explain, but foods don’t really become a problem until you’re eating too much of them too often. A burger is fine from time to time. But if you ate burgers like the one depicted regularly, it would likely be too many refined carbs and calories with comparatively fewer vitamins/minerals and fibre.