Is it English cucumber or Spanish onion onion?

That's a funny question! It seems like you're trying to make a joke about how some phrases sound strange when repeated.

There's no such thing as a "Spanish onion onion." The phrase is just a play on words, highlighting the redundancy of saying "onion onion."

Similarly, "English cucumber" is just a way to differentiate it from other types of cucumbers, though it's actually originally from India!