Bulgogi is a type of food. To make Bulgogi use thin tender strips of ribeye beef, and a sauce which is usually made with Soy-sauce, sesame oil, and juice from an asian pear (the 'apple shaped' yellow sort of pear) Some people still call it bulgogi if you use the sauce on other meats like pork, but other people say it's specific to beef-- and some even argue it's specific to the cut of beef like "steak" is in English. In any case it's delicious, and if you can you should try it. :D
For future reference, the korean sentence in passive form would look something like:
소고기 없이 불고기는 안 만들어져요
만들다 - make (active) 만들어지다 - be made (passive)
안 - not (is used instead of "못", cannot). In casual speech, 못 is mostly used for emphasis.
안 is also used to mean "cannot" especially in sense verbs like to hear, to see, to smell etc. and other verbs like to understand, or the one used in the example.
The interchangeability of these two words is quite similar to their use in English.
[With thanks to @TeoJr]