vegetarian shepherd’s pie with butternut squash

organic canola oil or avocado oil

large sweet onion

chopped mushrooms

chopped fresh oregano or marjoram

salt, divided

lentils, drained and rinsed (or 1 ½ c cooked lentils)

packed cup finely chopped spinach or chard leaves

large Roma tomato, chopped (about 1 cup)

water or vegetable broth

medium butternut squash, peeled, seeded and cut into large chunks

unsalted butter

plain Greek yogurt

shredded Gruyere cheese