Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Peel the sweet potato and cut it into uniform half-inch cubes for even roasting.
Toss the sweet potato cubes on the baking sheet with half of the olive oil, a pinch of sea salt, and a pinch of black pepper.
Roast the sweet potatoes for 20 to 25 minutes until they are tender and the edges are slightly caramelized.
While the potatoes roast, season the chicken breast with garlic powder and the remaining salt and pepper.
Heat the remaining olive oil in a skillet over medium-high heat and cook the chicken for 6 to 7 minutes per side until fully cooked.
Remove the chicken from the heat, let it rest for 5 minutes, then slice it into thin strips.
In a small bowl, whisk together the plain Greek yogurt and lemon juice until the dressing is smooth.
Place the mixed greens in a large bowl and top with the roasted sweet potatoes, sliced chicken, and crumbled feta cheese.
Drizzle the lemon-yogurt dressing over the salad and toss gently before serving.