Boil the potato until fork tender and allow to cool completely. Peel off the skin, quarter if necessary, and lightly smash with a fork. Set aside.

In a small pan, melt the butter for the topping and cook and stir in the panko until just starting to turn golden. Season with a pinch of salt and pepper. Set aside.

In a tall sided pan, cook the bacon over medium heat until crispy and browned. Transfer to a plate lined with paper towel. Reserve 1 tablespoon of the bacon grease in the pan. (Use avocado oil if omitting bacon.)

Add the onions and garlic and sauté for about 3-4 minutes, until soft and translucent. Add in the cabbage and sliced leek. Season with half the salt and pepper, and the red pepper flakes. Cook and stir for about 5 minutes more until soft.

Fold in the shredded potatoes, chopped bacon, and the white bottoms of the green onions, and turn off the heat. Transfer to a large bowl and set aside.

While cooking the pasta and making the sauce, preheat oven to 350ºF.

Cook the pasta according to package directions, just to al dente, not fully tender.

In the same pan as before melt the butter over medium heat. Whisk in the flour and stir for about 15 seconds to cook the flour through.

Slowly pour in the warm milk while whisking continuously, until all of the milk has been added and the butter/flour mixture has completely incorporated.

Reduce heat to medium-low and cook until thickened. Season with remaining salt and pepper, and the paprika. Once the sauce has thickened, remove from heat. Adjust seasoning if needed.

Mix the shredded cheese together and add to the sauce. Stir until the cheese has melted.

Fold in the cooked pasta and the cooked cabbage mixture until evenly combined. (For a creamier result, only add enough of the cabbage mixture so that the mixture is still nice and saucy.)

Transfer the mixture into an 8" square baking dish, oval casserole, or individual ramekins. Sprinkle the toasted panko over the pasta.

Bake for about 25 to 30 minutes, until bubbly. Serve warm and garnish with the tops of the green onions.