Ha, that's cool. You found a lot of different interpretations. These also exist in Dutch. No. 3 comes closest to how most people would understand the meaning in Dutch, but some others like no. 4 would fit too.
I read it as having meaning #2 but it depends on the intonation and context. If you emphasize fried then it's #3. If we're talking about having fried onions and not in your kitchen I'd probably assume #4.
Number 4 would be "Ik eet gefruite uien uitsluitend in mijn geruite keuken", though.
It mostly gets confusing for me because of moving back and forth between English and Dutch grammar, but any bit of context would make it a lot less ambiguous :)
