！
It's amazing he's so popular for just a tiny cameo role!
Literal
Just-a-tiny role [with-で] popular exist [nominalizer-の] [topic-は] amazing!
Otaku/fan enthusiasm register. ちょいやく (ちょい役) is an internet/fan slang term for 'a tiny role,' 'a minor cameo' — ちょい is a casual contraction of ちょっと ('a little'), and 役 is 'role, part.' ほんの ('just,' 'mere,' 'a mere X') is an attributive intensifier that minimizes the following noun — ほんのちょい役 = 'just a tiny role.' The exclamation is built on the cleft frame ~のはすごい ('X is amazing'). The sentence is vivid, colloquial fan-talk about a character or actor who gets disproportionate attention relative to their screen time.