Preheat oven to 350 degrees F (175 degrees C). Coat a 9x13 inch baking dish with nonstick cooking spray.
In a saucepan over medium heat, toast flour until golden. Stir in cornstarch, lemon pepper and onion powder. Gradually whisk in milk, then chicken bouillon. Cook, stirring, until sauce is thickened. Remove from heat, and stir in Cheddar cheese until smooth.
Layer potatoes and ham in prepared baking dish. Pour sauce evenly over potatoes and ham.
Bake in preheated oven for 1 hour. Let sit 5 minutes before serving.