Shred the cabbage and place it in a large bowl.
Slice the onion thinly in half moons.
Preheat the oven to 425˚ and line a rimmed sheet pan with parchment paper.
Add the onions, walnuts, salt and pepper to the cabbage and mix well.
Pour in the olive oil and maple syrup and toss well to coat the cabbage mixture.
Spread the mixture out on the parchment lined pan as evenly as possible, avoiding piles that are too thick. This will ensure the cabbage cooks quickly and evenly throughout.
Roast for 20-25 minutes or until you begin to see the cabbage turning brown.
Enjoy!