Preheat oven to 300 degrees F.
In a large bowl, whisk together Smoky BBQ, garlic, beer and Mexican oregano. Place the pork in the bowl with the spice marinade and massage into the pork. Add diced onion and mix well. Marinate for three to six hours.
Holding both ends of a banana leaf, slowly drag leaf over a burner on moderately high heat until the leaf slightly changes color and become shiny. Turn leaf over and toast other side in the same fashion, then repeat process with remaining leaves.
Line roasting pan with 3 of the toasted banana leaves, shiny side down. Let excess hang over sides allowing enough excess to cover pork. Transfer pork mixture to banana-lined pan and fold overhanging leaves over pork to enclose completely. Use a 4th leaf, if needed.
Roast for 4-5 hours, or until pork is tender and can be easily shredded with a fork. Allow pork to cool slightly, and shred into just larger than bite-sized pieces with two forks, and spread out on a cookie sheet.
Turn your broiler on high, and adjust the oven rack to the upper 1/3 of the oven. Broil the shreds of pork for just a few minutes, until the fat sizzles and the edges of the shreds become golden and crisp.ย
Serve as filling for tacos, alongside beans and rice or with classic American BBQ fare.