昼食と夕食の間隔が長いって英語でなんて言うの？

「昼食と夕食の間隔が長い」の直訳は The interval between lunch and dinner is longになります。

昼食 - lunch
夕食- dinner
間隔 - space, interval
長い - long

もっと自然な言い方だと
I eat breakfast at 7, I have lunch at 12 and then I have dinner at 9. There's a big gap between lunch and dinner.

...After I eat lunch I have to wait a really long time before (I have) dinner.

もしくは...I have a 9 hour gap between lunch and dinner になります。