"They like pasta a lot."
Translation:Ili multe ŝatas pastaĵojn.
I too am perplexed that they wanted a plural ending. I believe pasta is both singular and plural, and like fish/fishes, the plural should only be used when mentioning several kinds of pasta which was what Luis was saying (Saluton Luis).
If they had said 'They like pastas a lot', meaning all kinds of pastas, then I, like you, would have put the plural oj on the end.
TLTR: Tre is used for grade, multe for quantity. "Tre" should be correct in this instance (and that would be what would I use).