Caramelised Onion, Squash and Ricotta Tartines

medium butternut squash ((or other winter squash), ~1.5lbs)

olive oil

lemon juice

chili flakes

maple syrup

apple cider vinegar

small white or red onions (, or shallots, peeled and sliced)

salt

To serve: ricotta cheese (, sourdough bread (sliced and toasted))