Preheat oven to 350 degrees F.
Heat a large skillet on medium heat and add olive oil. To the pan, add the roast and brown each side of the roast (about 5 minutes). Set aside for a moment.
In a large roaster pan, add Marsala wine and the roast.
Sprinkle oregano leaves on top of the roast. With a cooking fork, lift up the roast a little and add some oregano leaves under the roast.
Sprinkle pepper and salt on top of the roast. Lift up the roast with a fork and add salt and pepper to the bottom of the pan...then lay the roast back down on top of it.
Top the roast with sliced garlic (and also put some under the roast in the bottom of the pan). Sprinkle the red hot pepper flakes on top of the roast.
To the top and around the sides of the roast, add onion.
To the pan, add carrots, Brussels sprouts, and potatoes. Add water to the pan around the edges of the roast.
To the vegetables and potatoes, add a few dashes of salt and pepper.
Cover the roaster pan with a lid. Bake in a preheated oven until tender (about 2-1/2 hours).
With two forks, shred the meat and serve warm with the vegetables and potatoes.
Top the meat and vegetables with juice from the pan.