Preheat your oven to 400°F and line a large sheet pan with parchment paper for easy cleanup.
Dice the russet potato, sweet potato, and carrots into uniform 1-inch cubes to ensure they cook at the same rate.
In a small mixing bowl, whisk together the olive oil, lemon juice, lemon zest, minced garlic, dried oregano, sea salt, and black pepper.
Place the chicken breasts and the chopped root vegetables onto the prepared sheet pan.
Pour the lemon-herb marinade over the chicken and vegetables, using your hands or tongs to toss everything until thoroughly coated.
Arrange the ingredients in a single layer on the pan, making sure the chicken pieces have space around them to roast properly.
Bake for 25-30 minutes until the chicken reaches an internal temperature of 165°F and the vegetables are tender and slightly caramelized.