Preheat the oven to 325 degrees F.
Add the olive oil, sage, rosemary, fennel seeds, garlic cloves, 1 teaspoon salt and 2 teaspoons pepper to a mortar and pestle. Mash until a paste forms.
Use a sharp knife to butterfly the pork. Follow the seams to open it up. Rub the meat with the paste into the inside cut. Drizzle the top with olive oil and sprinkle with salt and pepper. Roll and tie the pork, using kitchen twine, to make a compact shape. Add the head of garlic and the potatoes, cut-side down, to the roasting pan. Drizzle lightly with olive oil, and then place the pork on top, fat-side up.
Place in the oven and roast until the skin is brown and the meat is extremely tender, about 5 hours. While it roasts, use a rosemary sprig to occasionally brush the meat with some additional olive oil while it cooks, every 40 minutes or so.
Remove from the oven and let rest for 20 minutes before slicing. Remove the kitchen twine before slicing into 1/2-inch pieces. Remove the garlic from the pan to cool.
Heat a grill to medium-high heat.
Drizzle the peppers with a bit of olive oil, salt and pepper. Grill until tender, flipping half way through, about 4 minutes per side.
Use the juice from the bottom of the roasting pan to brush the bread. Grill the bread until golden brown. Top the bread with sliced pork, grilled peppers, arugula and roasted garlic if desired. Slice into desired servings.
The garlic will be soft after the slow roasting. Use it to spread on your bread. The potatoes are a nice cook's treat - eat them as a snack while you wait for your pork to rest.