one serving; one pile; one helping
Refers to a single portion or heap of something, often food served on a plate or in a bowl. The counter 盛り is used for servings, and 一盛り emphasizes one such portion.
One serving of sashimi, please.
彼はご飯を一盛りぺろりと平らげた。
He polished off one helping of rice in no time.
Compound of 一 (ひと, 'one') and 盛り (もり, 'serving, heap'), the noun form of 盛る (もる, 'to pile up, serve').