Put peeled potatoes and the scallions into the pot and add just enough water to cover. Bring to a boil and cook for 30 minutes or until tender. Drain.
***While potatoes are cooking***
Add olive to heated skillet. Saute onions and tomatoes until they are tender.
Add the milk, cheese, salt, and pepper. Stir to combine. Turn down the heat and let the sauce thicken.
To serve, place drained potatoes on a large serving platter in a single layer. Pour sauce over top, and make sure each potato has some sauce on it. Garnish with sliced green onions or chopped chives.