Preheat the oven to 425 degrees F. Place the oven rack in the middle. Butter bread slices on both sides. Arrange on a greased baking sheet. Place into the oven and bake for 10 minutes or until toasty. Flip the bread slices after 6 minutes. Keep an eye on them so they don’t burn. Remove from the oven.
In a medium bowl whisk together eggs, milk, and black pepper until blended. Stir in green pepper, ham, and onions.
Spray an 8-inch nonstick skillet with cooking spray. Pour the egg mixture into the skillet. Cover. Cook on medium heat for 6 minutes or until the egg mixture is set but the top is still slightly moistened. Occasionally left the edge with a spatula and tilt the skillet to allow the uncooked portion to flow underneath. Sprinkle cheese onto half of the omelet. Split a spatula underneath the omelet, tip the skillet to loosen and gently fold the omelet in half. Remove from heat and let stand, covered, for 2 minutes.
Cut the omelet in half. Fill the toast slices with the omelet halves to make 2 sandwiches.