In a large covered casserole or crock pot, drizzle the oil.
Place 1/2 the chopped onions, mushrooms, sun-dried tomatoes, parsley, capers and a little marinara sauce in the casserole.
Place the meat on top and season well with salt and pepper.
Layer the remaining onion, mushrooms, sun dried tomatoes, parsley, capers and marinara sauce on top.
Cover dish and place in a 260 degree oven for 5 to 6 hours depending on the thickness of your cut of meat. It should be falling apart when it is ready. It might be wise, if you are using a thick hunk of meat, to cut it into pieces before assembling and cooking the dish.
Shred the meat, remove any bones and large pieces of fat and discard them, drain off the liquid fat (I do this into a bowl which I refrigerate so I can retrieve the non-fatty part that sinks to the bottom). Stir it around to distribute the ingredients.
Sprinkle with the olives and feta cheese.
Serve over pasta, rice or with a French baguette with a nice Romaine salad and a good glass of Cabernet Sauvignon.