Preheat your oven to 400°F and line a small baking sheet with parchment paper.
Peel the russet potato and cut it into uniform 1-inch cubes for even cooking.
Place the potato cubes in a medium pot, cover with water, add 0.25 tsp sea salt, and bring to a boil.
Boil the potatoes for 12-15 minutes or until they are completely fork-tender.
While potatoes cook, rub the chicken breast with olive oil, dried oregano, 0.25 tsp sea salt, and black pepper.
Roast the chicken in the oven for 18-22 minutes until the internal temperature reaches 165°F.
Mince the garlic cloves and sauté them in a small pan with the grass-fed butter over low heat for 1 minute until fragrant.
Drain the cooked potatoes thoroughly and return them to the warm pot to allow excess moisture to evaporate.
Add the garlic butter, Greek yogurt, and grated Parmesan cheese to the potatoes.
Mash the mixture vigorously until the potatoes reach a smooth and creamy consistency.
Slice the roasted chicken and serve it immediately over the bed of buttery garlic mashed potatoes.