small cup, small bowl
盅 centers on a small open container for drinking or serving: a small cup or bowl.
盅 combines 皿 (dish, bowl) with 中, which likely contributes a phonetic element. The character is used for small drinking vessels.
The top 中 looks like a small cup placed right in the middle of the bottom dish 皿. Together they form a small bowl or cup.
For チュウ, imagine a tiny cup of chowder: chow -> チュウ, and the small bowl holds just enough.