Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel the sweet potato and cut it into uniform 1/2-inch cubes, then slice the chicken breast into bite-sized strips.
On the baking sheet, toss the chicken and sweet potatoes with 2 teaspoons of olive oil, garlic powder, smoked paprika, sea salt, and black pepper.
Spread the mixture in a single layer and roast for 20 to 25 minutes until the chicken is cooked through and the potatoes are tender and golden.
While roasting, whisk together the remaining 1 teaspoon of olive oil, lemon juice, and Dijon mustard in a small bowl to create the vinaigrette.
Place the arugula in a large serving bowl and lightly toss with half of the prepared lemon-Dijon dressing.
Add the warm roasted chicken and sweet potatoes to the bowl of greens.
Top the salad with the crunchy pumpkin seeds and drizzle with the remaining dressing before serving immediately.