Preheat the oven to 400 degrees. Spread the butternut squash noodles out on a baking sheet, drizzle with olive oil and season with garlic powder, salt and pepper. Line another baking tray with parchment paper and place the walnuts. Bake the butternut squash noodles alongside the walnuts, baking the walnuts for just 5 minutes and baking the noodles for 8-10 minutes or until al dente, tossing halfway through.

While the butternut squash is baking, shred the brussels sprouts. Chop the bottoms off and peel off the outer leaves, if tough and discolored. Slice them in half and then slice thinly lengthwise. Set aside.

Place a large skillet over medium heat and add in the olive oil. Once oil is shimmering, add in the garlic, red pepper flakes and onion and lower heat to medium-low and cook the onion, stirring occasionally, until onion is translucent and mainly wilted, about 3 minutes.

Add in the brussels sprouts and season with salt and pepper. Cover and cook the brussels sprouts, still on medium low heat, uncovering occasionally to stir, or until lightly browned and cooked (about 3-5 minutes). Take the skillet off the heat and add the parmesan (if adding) and then fold in the walnuts, stir, and pour into a large mixing bowl along with the butternut squash noodles.

Toss to combine and serve.