Thanking professor with dinner delivery
I would avoid giving food-- especially a full meal-- to a professor, unless you know them very well. This is because you may not know their tastes or dietary requirements; for instance, unwittingly giving them a dish with nuts in if they have a severe allergy is definitely not a good idea.

It's also a bit strange to deliver such a meal to their office. They probably want to go home and eat their dinner there, rather than sit in the office and eat your gift.

While you are understandably grateful for the reference letters, the professor probably just considers this part of their job. If you really want, a nice handwritten card saying thank you would certainly suffice.