Carefully, slice a thin layer off of the bottom of each potato, and discard the strip. This should allow the potato to stand with east. Place two wooden spoons on either side of the potato, these will be your knife guard. Slice the potato at even intervals, about 1/8th of an inch, to create a scalloped pattern, not allowing the knife to go below the spoons (the goal is to not slice completely through the potato).
Swirl a bit of olive oil in an oven safe skillet and arrange the potatoes so they are nestled into the pan. Arrange a paper thin piece of butter into every slice. Let the potatoes bake for about 45 minutes.
Carefully remove the potatoes from the oven, to top before finishing off. Spoon a heaping dollop of marinara over each potato from side to side. Arrange the mushrooms, peppers and diced onions over each, using a spoon to pat down in place so they stay on top, and finally, sprinkle with mozzarella cheese. Finish cooking the potatoes in the oven for another 10 to 15 minutes.
Carefully remove the skillet from the oven and sprinkle the crumbled bacon over top. Wait 5 minutes before serving to your hungry audience.