Preheat oven to 350°. In a large skillet, cook bacon over medium heat until crisp. Drain, reserving 1 tablespoon drippings. Set bacon aside. Saute onions in drippings until tender; set aside.
In a large bowl, beat eggs. Add milk, seasoned salt, 2 cups cheese, bacon and sauteed onions. Transfer to a greased shallow 2-qt. baking dish.
Bake, uncovered, 35-40 minutes or until set. Sprinkle with remaining cheese. Freeze option: Freeze unbaked omelet until firm; cover with foil. To use, remove from freezer 30 minutes before baking (do not thaw). Preheat oven to 350°. Bake as directed, increasing time as necessary for a knife inserted in the center to come out clean. Sprinkle with 1/2 cup cheese.