Preheat your oven to 400°F and line a small baking sheet with parchment paper.
Peel the Yukon Gold potato and cut it into 1-inch cubes to ensure even cooking.
Place the potato cubes in a pot of cold water, bring to a boil, and simmer for 12 to 15 minutes until fork-tender.
While the potatoes boil, mince the fresh garlic cloves, rosemary, and thyme.
In a small bowl, combine the olive oil, minced garlic, rosemary, thyme, sea salt, and black pepper.
Rub the herb oil mixture thoroughly over the chicken breast and place it on the prepared baking sheet.
Roast the chicken for 18 to 22 minutes, or until the internal temperature reaches 165°F and the juices run clear.
Drain the cooked potatoes and return them to the warm pot, then add the Greek yogurt and garlic powder.
Mash the potatoes vigorously until they reach a velvet-smooth consistency, adjusting with a splash of water if needed.
Slice the roasted chicken into thick medallions and serve immediately over the warm mashed potatoes.