Question

add a comma or semicolon if needed. otherwise, submit the text without any additional punctuation. if you dont have leeks for this dish, try onions instead or use shallots if theyre available.

Explanation:

The sentence has two independent clauses ("try onions instead" and "or use shallots if they're available") connected by "or". A comma should be used before "or" to separate the clauses.

Answer:

If you don't have leeks for this dish, try onions instead, or use shallots if they're available.