It's a cucurbit. OP, just so you know, self-seeding cucurbits are fairly often sterile, so it might not produce anything very exciting! (I learned this from bitter experience after buying some squash seedlings from a village stall - I tended them carefully and watched them develop into beautiful lush plants that did absolute bugger all. The woman I bought them from told me she'd just planted seeds from her home-grown squash and and labelled them as if they were the parent plant. She didn't know either.)