In a bowl, stir together the Dark Brown Sugar (3 tablespoon), Onion Powder (1 tablespoon), Garlic Powder (1 tablespoon), Chili Powder (1 tablespoon), Dried Oregano (1 tablespoon), Paprika (2 tablespoon), Ground Black Pepper (1 teaspoon), Cayenne Pepper (1 teaspoon), Salt (8 teaspoon).
Rub the mixture all over the Pork Shoulder (7 pound). Wrap the pork in plastic wrap and refrigerate for several hours or overnight.
Preheat the oven to 300 degrees F (150 degrees C). Cut the Onion (4) into thick slices and place them on the bottom on a large baking pan. Place the Pork Shoulder in the large baking pan.
Cover with aluminum foil. Roast until fork-tender and falling apart, 6-7 hours. Remove the pork from the pan and set it on a cutting board.
Shred the pork with two forks, then mix with Barbecue Sauce (2 cup).
Serve on Hamburger Bun (to taste), and coleslaw if desired.