Preheat oven to 350 degrees. Spray 3-quart casserole/baking dish with non-stick spray.
Layer half of potato slices in bottom of prepared pan; top with half of onions. Season this layer with 1/2 of salt, pepper and garlic powder. Place half of the ham cubes on top of onion layer. Repeat layers saving some onion to place on top of second ham layer, seasoning each vegetable layer.
Combine cheddar cheese and mushroom soups in a medium bowl. Add water and stir to combine well. Pour over potato, onion and ham layers. Top with reserved onion slices. Cover with foil and bake for 1 hour and 15 minutes. Remove foil and sprinkle top with 1/2 cup of Panko bread crumbs. Return to oven and continue baking for 15 more minutes until top is golden brown.