Prepare the tart's bacon "crust" by taking a small cast iron pan and covering the bottom of the pan with a pinwheel of bacon. Each bacon slice should have one end at the center of the pan with about half of the slice extending over the edge of the pan. (That overhang will later be folded back to form the top layer of the "crust".) Overlap bacon slices slightly until entire pan bottom is covered.
Add layer of potato slices, then layer of cheese, then potatoes, then cheese, and so on until ingredients are used and pan is filled.
Fold the bacon slices that are hanging over the edge of the pan back over the layers of potatoes and cheese towards the pan's center to form another pinwheel as the top "crust" of the tart.
Place potatoes, celery, and carrot in a large pot and cover with water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain and transfer to a 2-quart baking dish.
Melt 3 tablespoons butter in a large skillet over medium heat; cook and stir ham, green bell pepper, and onion until vegetables are tender, about 5 minutes. Transfer ham mixture to baking dish and mix with potatoes, etc.
Melt remaining 1/4 cup butter in a clean skillet; cook and stir flour in melted butter until smooth, about 3 minutes. Gradually stir in milk and season with salt and black pepper. Bring to a boil, stirring constantly, until thickened, about 2 minutes. Add Cheddar cheese; stir until melted. Pour cheese mixture over ham and potatoes. Sprinkle with bread crumbs.
Bake in preheated oven until bubbly, 25 to 30 minutes. Allow casserole to rest for 5 to 10 minutes before serving.
Line two 15-in. x 10-in. x 1-in. baking pans with foil and coat with cooking spray. Add potatoes, carrots, turnip and onion; generously coat with cooking spray. Bake, uncovered, at 425° for 25-30 minutes or until tender.
Arrange ham slices over the vegetables. In a bowl, combine remaining ingredients. Spoon over ham and vegetables. Cover and bake 10 minutes longer or until the ham is heated through.