To make the stuffing, heat the olive oil in a skillet over medium heat.
Next add garlic, onion, sage, rosemary, thyme and mushrooms.
Season the mushroom mixture with salt and then sauté until softened, about 10-12 minutes.
Add the spinach to the pan and toss.
Remove from the heat and let cool.
Preheat the oven to 375 °F.
To begin making the pork roast, place the meat on a cutting board.
Cut the pork by slicing at an angle, away to your cutting board, and then keep slicing lengthwise to cut into the pork to slowly ‘unroll’ it.
Lay the piece of meat open then cover with plastic wrap to avoid meat splatter.
Using a meat mallet, pound the meat to about 3/4 inch thickness then set aside.
On a piece of parchment paper, arrange prosciutto slices in a single layer but so the edges overlap.
Sprinkle chopped sage leaves on top of the prosciutto.
Season the pork with salt and place on top of the prosciutto slices.
Spread the stuffing evenly over the meat.
Roll up the pork and tie in intervals with twine to secure.
Tuck a rosemary sprig into the twine, on top of the pork loin.
To make the brussel sprouts, toss them and the remaining onions in a roasting pan together with the garlic and olive oil.
Season the sprouts with salt.
Set the roast on top.
Roast until the internal temperature reaches 145 degrees, 1 hour to 1 hour 15 minutes.
Slice the roast and serve alongside the brussel sprouts.
Garnish with fresh sage and thyme.