Preheat oven to 400° Fahrenheit (200° Celsius).

Transfer peeled and diced potatoes into a pot and pour water in. Use just enough water so they all are submerged. Add salt. Cover with a lid and bring to a boil. Then, reduce the heat to low and simmer until they are almost done.

Meanwhile: Heat oil in a large frying pan and add onion. Sauté until translucent, about 4 minutes. Add fresh spinach in stages and sauté until all leaves are wilted. Stir in minced garlic and cook until it releases its aroma. Turn off the heat.

In a small bowl, mix together sour cream, salt, black pepper, oregano, and garlic powder until smooth.

Drain the water from the potatoes and combine them with the spinach and sour cream mixture. Pour the mixture into an oven-proof dish and cover with grated cheese.

Cook at 400° Fahrenheit (200° Celsius) until the cheese is golden brown and potatoes soft, about 25 minutes.