Preheat the oven to 400°F. Peel and cube the sweet potato, toss it lightly in olive oil, salt, and pepper, and spread it out on a baking sheet.
Place the sweet potatoes in the oven and roast for about 20-25 minutes until tender and lightly crispy on the edges.
While the sweet potatoes roast, season the chicken breast with a pinch of salt, pepper, and cinnamon.
Heat a non-stick skillet over medium-high heat and sear the chicken for 2-3 minutes per side until golden.
In a small saucepan, combine the diced apple, apple cider, and a pinch of cinnamon. Allow the mixture to simmer for 3-4 minutes until the apples soften and the glaze thickens slightly.
Pour the apple glaze over the seared chicken, reducing the heat to a gentle simmer for another 3 minutes to meld the flavors.
Plate the apple-glazed chicken alongside the roasted sweet potatoes and sprinkle the crisp walnut crumble over the top for added crunch.
Finish with an extra pinch of black pepper if desired and serve immediately.