I'm surprised you can eat it even though it's quite peppery.
「結構胡椒のパンチが効いてるけど、よく食べてるね」は英語で I'm surprised you're able to eat it even though it's quite peppery/spicy もしくは I'm surprised you can eat it even though it's got a really strong black pepper flavour になると思います。
パンチ - punch/ packs a punch
例えば、
- These drinks are quite fruity but they really pack a punch.
この場合は drink = アルコールが入っている飲み物です。
- His speech lacked punch.
peppery - ピリッとする/ 胡椒の効いた~