House Elves were cooking all the food, and Dumbledore kept saying "Let's eat", and all the food magically appeared on plates. Was he using mass teleportation every day to perform that trick?
Harry’s theory is the food is sent through the ceiling to the tables.
When Hermione took him down to the kitchens, Harry notices tables set up exactly like the ones in the Great Hall above.
“‘Yes, sir, yes!’ said Dobby, and he seized Harry’s hand, and pulled him off into the kitchen between the four long wooden tables that stood there. Each of these tables, Harry noticed as he passed them, was positioned exactly beneath the four house tables above, in the Great Hall. At the moment, they were clear of food, dinner having finished, but he supposed that an hour ago they had been laden with dishes that were then sent up through the ceiling to their counterparts above.”
- Harry Potter and the Goblet of Fire, Chapter 21 (The House-Elf Liberation Front)
Harry theorizes that the food is sent up through the ceiling to the tables in the Great Hall. While Harry is certainly not infallible and can be wrong, this seems like a sound presumption. However, it's unclear exactly how the food is sent up through the ceiling. It could be Dumbledore doing it, the house-elves doing it, or the tables could be enchanted to do it themselves.
This occasion in the Great Hall shows the food getting into the Great Hall after it's revealed that the food was made by house-elves, but it doesn't make it clear exactly who or what transports the cooked food up to the Great Hall.
“The Tournament will be officially opened at the end of the feast,’ said Dumbledore. ‘I now invite you all to eat, drink, and make yourselves at home!’
He sat down, and Harry saw Karkaroff lean forward at once and engage him in conversation.
The dishes in front of them filled with food as usual. The house-elves in the kitchen seemed to have pulled out all the stops; there was a greater variety of dishes in front of them than Harry had ever seen, including several that were definitely foreign.”
- Harry Potter and the Goblet of Fire, Chapter 16 (The Goblet of Fire)