Coat a 9-inch x 13-inch baking dish with nonstick cooking spray.
Heat the vegetable oil in a small skillet over medium heat. Add the bell pepper and cook, stirring, for 2 to 3 minutes or until fork tender. Remove skillet from the heat and set aside.
Combine the ham, half of the green onions, the bell pepper, and one package Sargento Shreds in a large mixing bowl. Cover and refrigerate remaining half of the green onions. Scoop about 1/3 cup of the ham and cheese mixture onto each tortilla and roll them tightly. Place the filled tortillas seam side down in the prepared baking dish.
Whisk together the eggs, half-and-half (or whole milk), seasoning salt, and flour, and pour the mixture evenly over the enchiladas. Cover the dish with foil and refrigerate overnight.
The next morning, remove the baking dish from the refrigerator and let it rest on the kitchen counter while you preheat the oven to 350 degrees F.
Bake, covered, for 35 minutes. Remove the foil and sprinkle remaining cheese over enchiladas. Bake for 10 more minutes or until tops are golden brown and the egg mixture is set.
Garnish with reserved green onions and serve with salsa and sour cream on the side.