Peel the Yukon Gold potato and cut into 1-inch cubes.
Place potato cubes in a pot of cold water with a pinch of salt, bring to a boil, and cook for 12-15 minutes until fork-tender.
While potatoes boil, season the chicken breast with dried oregano, half of the sea salt, and half of the black pepper.
Heat olive oil in a skillet over medium-high heat and sear the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
Mince the garlic cloves and gently melt the grass-fed butter in a small pan over low heat, adding the garlic for 1 minute until fragrant but not browned.
Drain the cooked potatoes and return them to the warm pot.
Add the garlic-butter mixture, Greek yogurt, remaining salt, and remaining pepper to the potatoes.
Mash until smooth and creamy, then stir in the chopped fresh chives.
Slice the chicken and serve it immediately over the warm mashed potatoes.