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.
Notes
Be sure that your hash browns have thawed before you cook them. Otherwise, they take a very long time to bake. You can defrost them in the microwave to speed up this process, and pat them dry to remove excess water. Or take them out of the freezer and let them thaw in the refrigerator overnight.