What kind of squash have you grown? Or thrown into your compost? Looks pumpkin-ish to me, but I know there are many types of round summer and winter squash. This years volunteer in my compost looks to be a butternut squash, even though I haven't grown any or bought any from the store.
I have thrown squash in the compost . . . including yellow crook neck, zucchini, acorn, patty pans, butternut, spaghetti. . . pretty much every variety ended up in my compost last year from scraps and such.
I also have a massive pile of tomato volunteers and a watermelon volunteer.
Could be spaghetti. I'm growing it for the first time this year and have some that looks like that. But I'm also growing butterup and sugar pumpkins and I'm guessing what each one is since I forget what I planted where.
Rather looks pumpkin-ish to me as well. There is a round zucchini, but I think the others you mentioned look different from the start. Then, there is the possibility you have a cross of different squash growing there.