Preheat oven to 400°F. Peel butternut squash, cut down the middle lengthwise and spoon out the seeds and slice into ½ inch thick slices.
Drizzle avocado oil over squash, then season with kosher salt and freshly cracked pepper and place on a baking sheet.
Place in oven and cook for 20 minutes or until browned and tender.
While butternut squash is roasting, start on the brown butter.Melt butter in a saucepan then add sage. Keep a consistent stir and swirl of the pan. Add ¼ teaspoon kosher salt and a pinch of black pepper. Keep swirling until butter begins to brown. You'll notice foam start to form, then subside. Once honey-colored milk solids begin to form along with a nutty aroma, remove from heat.
Once squash is perfectly roasted, place on a serving plate. Spoon brown butter sage sauce over butternut squash. Top with freshly grated parmesan. Serve!