Preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the cubed sweet potatoes with 1 teaspoon of olive oil and a pinch of salt, then spread them in a single layer on the baking sheet.
Roast the sweet potatoes for 20 to 25 minutes until they are tender and slightly browned.
While the potatoes roast, season the chicken breast with dried oregano, salt, and pepper.
Grill the chicken over medium-high heat for about 6 to 7 minutes per side or until the internal temperature reaches 165°F.
In a small bowl, whisk together the Greek yogurt, lemon juice, and the remaining half teaspoon of olive oil to create a creamy dressing.
Slice the grilled chicken into strips and thinly slice the apple.
Place the mixed greens in a large bowl and top with the roasted sweet potatoes, grilled chicken, and apple slices.
Drizzle the creamy lemon-herb dressing over the salad and toss gently before serving.