Preheat the oven to 375 degrees F. Pour a thin coat of oil in a skillet and heat to medium. Add the spinach and cook until wilted. Drain in a colander, pressing out as much water as you can. Return to a bowl and add the sour cream, salt, and pepper to taste and the cayenne pepper. Place in a buttered or oiled casserole and top with the cheese. Bake until the cheese is melted.