expression
quite a chore; not that easy; fairly difficult
Colloquial phrase expressing that something is surprisingly or unexpectedly hard work or more difficult than it looks.
毎日自炊するのは結構大変だよね。
Cooking for yourself every day is quite a chore, isn't it?
この問題、結構大変だったけど、なんとか解けた。
This problem was fairly difficult, but I managed to solve it.
Combination of 結構 (けっこう, 'quite, surprisingly') and 大変 (たいへん, 'difficult, hard'). The phrase is a natural collocation, not a fixed idiom.