Preheat oven to 475 degrees. Combine garlic, oregano, salt and pepper. Make inch deep gashes all over the roast and fill with the garlic mixture. Rub the roast all over with salt and pepper. Place in shallow roasting pan and bake for 20 minutes. Lower heat to 350 and bake for 2 hours. Remove from oven and let rest 20 minutes. Carve into slices. Warm the rolls in oven and slice in half lengthwise. Remove some of the inside bread to make room for sandwich contents. Spoon 2 tablespoons salsa over each bun, add pork slices. Drench with more sauce. Add tablespoon sour cream and garnish with avocado. Serve open faced.