Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Peel and dice the sweet potato into 1/2-inch cubes, and cut the chicken breast into bite-sized pieces.
Place the sweet potatoes and chicken on the baking sheet; drizzle with 0.5 tbsp of olive oil and season with garlic powder, smoked paprika, and half of the salt and pepper.
Toss well to coat and spread in a single layer, then roast for 20-25 minutes until the chicken is golden and the sweet potatoes are tender.
While roasting, prepare the dressing by whisking together the remaining 0.5 tbsp of olive oil, lemon juice, Dijon mustard, and the remaining salt and pepper in a small bowl.
In a large serving bowl, combine the baby spinach and diced red bell pepper.
Add the warm roasted chicken and sweet potatoes to the bowl, drizzle with the lemon-Dijon vinaigrette, and toss gently until the greens are slightly wilted and everything is well combined.