Thanks! Yeah, his one favorite meal that survived the shift is refried beans on corn tostadas. (He still calls them "beans and cheese" even though there hasn't been cheese on them for months.) I'll have to try the squash mixture--although I'll probably have to sell him on it as a "cheese dip" at first.
I also read somewhere that one woman uses spaghetti squash (the kind that you tear out of the shell with a fork and it separates into these little strands like spaghetti) as the "cheese" on her kid's pizza. Another said she used grated polenta.