Preheat oven to 375 degrees F.
Dice onion as finely as you can.
Mix together ground turkey with onion, add salt ant pepper to taste.
Place the turkey mix in an even layer on the bottom of a 9x13 inches baking dish.
Peel and shred potatoes.
Spread the shredded potatoes evenly over turkey.
In a small bowl, whisk together sour cream, eggs and water. Add 1/2 tsp of salt.
Evenly pour the egg mixture over casserole and sprinkle with cheddar cheese.
Bake uncovered for 55 minutes, or until a knife inserted near the center comes out clean.
Serve it hot with sour cream and cilantro.