Preheat the oven to 400 degrees F.
Cut the potato in half length-wise, then slice into about 1/4-inch slices. Place the potato wedges into a large bowl. Add the olive oil, salt, pepper and garlic powder and toss to coat well.
Place the potatoes onto a large baking sheet and roast in the oven for about 30 minutes or until tender, turning the potatoes over after about halfway through roasting. Place the pan under the broiler for a few minutes just until lightly charred.
Meanwhile, melt the butter in a medium saucepan over medium heat. Stir in the flour.
Stir in the milk and chicken stock until well blended. Stir in the bell pepper, onion and garlic. Cook for about 3 or 4 minutes, stirring occasionally.
Stir in the Provolone, Parmesan and cream cheeses. Cook for another 3 to 4 minutes or until the cheeses are melted, The sauce should be a little thick. If it is too thick, add some chicken stock. If it is too thin, add a little flour and let cook another minute. Salt and pepper to taste.
Arrange the potatoes on a large plate or serving dish. Top with corned beef and cabbage (see tip). Pour the cheese sauce over top. Garnish with sliced jalapenos and/or sliced green onions, if desired optional. Serve immediately.