Peel the potato and cut into 1-inch cubes, then place in a pot of cold salted water and bring to a boil.
Cook the potatoes for 12-15 minutes until fork-tender, then drain and return to the pot.
While potatoes boil, season the chicken breast on both sides with dried oregano, half the sea salt, and half the black pepper.
Heat half of the ghee in a non-stick skillet over medium-high heat and sear the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
Remove the chicken from the pan to rest, and in the same skillet, add the spinach and a splash of water, sautéing for 1-2 minutes until wilted.
Mince the garlic and add it to the drained potatoes along with the Greek yogurt, almond milk, remaining ghee, and remaining salt and pepper.
Mash the potato mixture until smooth and creamy.
Plate the creamy garlic mashed potatoes, top with the sliced chicken breast, and serve with the wilted spinach on the side.