Pasta With Collard Greens and Onions

bunch collard greens, stemmed and washed

extra virgin olive oil

medium onion, preferably a red onion, cut in half lengthwise, then sliced across the grain

Salt

red pepper flakes (optional)

garlic cloves, minced, or 1/2 head green garlic, stalks and papery shells removed, sliced

Freshly ground pepper

to 12 ounces pasta, any shape

cooking water from the pasta

to 2 ounces Parmesan (to taste)