Bass Agrodolce with Spaghetti Squash and Mushrooms

extra-virgin olive oil

or 4 sprigs fresh rosemary

head garlic, peeled

red pepper flakes

red wine vinegar

sugar

medium spaghetti squash

Kosher salt and freshly ground pepper

mixed mushrooms (shiitake, chanterelle and/or oyster), cut into pieces if large

cherry tomatoes

striped bass fillets, pin bones removed