Make the mac and cheese and then pour it into a parchment lined 5x7 baking dish. Cover with more parchment, pressing down to compact the mac. Cool in the fridge for 3 hours. Flip the mac and cheese out so it is upside down on a piece of parchment that used to be on top. Remove the parchment form the top and return to the fridge for 1 more hour.
Slice the spam 1/2 inch thick and add it to a frying pan. Sear on both sides, about 5 minutes per side. There is extra spam but it's really good so that's fine.
Meanwhile, make the sauce by mixing together the sauce ingredients. Pour this sauce over the spam and stir to coat. Allow to simmer with the spam, flipping occasionally, until the sauce it thick and starting to caramelize. Remove from heat.
Use parchment paper to trace the shape of the spam, then cut out 3 pieces of mac and cheese the same size. Be careful as you cut to get clean lines and not have the mac and cheese falling apart. Sprinkle some togarashi over the mac and cheese.
Toast the nori over a burner that is turned on high (electric will work too!) just for a second or two.
Slice the nori into 3 strips. Place a slice of spam on each mac and cheese piece. Wrap the nori around the "macsubi" and seal at the bottom with a dab of water. Serve