Step 1: Preheat the Oven
1. Preheat Oven: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper for easy cleanup.

Step 2: Prepare the Sweet Potatoes
1. Combine Ingredients: In a large bowl, toss the sweet potato cubes with olive oil, maple syrup, cinnamon, salt, and black pepper until well coated.

Step 3: Roast the Sweet Potatoes
1. Arrange on Baking Sheet: Spread the sweet potatoes in a single layer on the prepared baking sheet.
2. Roast: Roast in the preheated oven for 20 minutes.
3. Add Walnuts: After 20 minutes, remove the baking sheet from the oven and add the chopped walnuts. Toss gently to combine.
4. Continue Roasting: Return to the oven and roast for an additional 10-15 minutes, or until the sweet potatoes are tender and caramelized, and the walnuts are toasted.

Step 4: Serve
1. Garnish: Remove from the oven and let cool slightly. Garnish with fresh parsley or thyme if desired.
2. Enjoy: Serve warm as a side dish to your favorite main course.