Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Scrub the russet potato thoroughly and cut into 1/2-inch cubes, ensuring they are uniform for even roasting.
In a mixing bowl, toss the potato cubes with 0.5 tablespoons of olive oil and half of the oregano, garlic powder, salt, and pepper.
Spread the potatoes in a single layer on the prepared baking sheet and roast for 15 minutes.
While potatoes are roasting, trim the ends of the green beans and season the chicken breast with the remaining olive oil and spices.
Remove the baking sheet from the oven, slide the potatoes to one side, and place the chicken breast and green beans on the other side.
Return the pan to the oven and roast for an additional 18 to 22 minutes, or until the chicken reaches an internal temperature of 165°F.
Remove from the oven and immediately squeeze the fresh lemon juice over the chicken, potatoes, and beans before serving.