Preheat oven to 350 degrees.
Pour the olive oil into a skillet and bring it to medium-high heat. Cook the hash browns, onions, and salt to taste until the hash browns are tender and brown. Drain the hashbrowns on a plate covered with paper towels. Set aside.
Next, in a separate bowl, mix together 1 1/2 cups of the cheese and the cream of chicken soup. Add the hash browns to the mixture.
Transfer the mixture into a buttered 2 qt. casserole dish, and sprinkle the rest of the cheese over the top. Cook at 350 degrees for 30 minutes or until golden brown. The cheese should be nice and crispy.