Bring a pot of salted water to a boil. Add the string beans and cook for 4–6 minutes, until tender but still bright green.Drain well and let cool slightly.
In a large bowl, combine the cooked string beans and the cooked corn.
Drizzle with the olive oil and lemon juice. Add the red pepper flakes and a pinch of salt.
Toss gently until everything is evenly coated.
Add the chopped parsley and dill and toss again.
Gently fold in the crumbled feta cheese.
Taste and adjust the seasoning with additional lemon juice, salt, or pepper flakes if needed.Serve immediately, at room temperature, or chilled.