Plataea : nf fam. Content of a dish (usually simple), served abundantly.
A (good) dish of mash or noodles.
The expression “a plateful/plastered (of food)”: A large quantity, a very abundant ration (of food).
The content of a dish bears, since the XNUMXth century, the name of plate, used mainly in connection with simple and rustic foods, therefore with a somewhat pejorative meaning.
This word quickly came to colloquially refer to “a large quantity”, but not only food.
A plateful of floury foods "stuffs" the stomach while being not very nourishing, like a cast that one would dare to swallow (the cast being the quantity of plaster that one is in preparing).
It is probably this kind of comparison, the resemblance of the words and the pleasantness of the expression which made it use the word plastered instead of plate towards the end of the XNUMXth century.
About the belly, it is simply the quantity contained in the belly (the stomach), with an implication of exaggeration, the belly giving the impression of being ready to explode.
– Quote from the American writer John Fante (1909-1983): “Soon the whole downstairs of the hotel began to smell the pungent aroma of grilled liver with onions. I went to see him at his house. He was sitting in front of a plate of meat, his mouth all smeared. » in the novel Ask the Dust (ask the dust) (1939).