Although cooking onions in a smoker take some time, the process adds a flavorful smokiness that contrasts with their natural sweetness. Whether you chop, slice or leave them whole, the process is simple -- the onions cook slowly, wrapped loosely in aluminum foil, over your favorite wood chip flavor for up two hours. The smoked onions will complement just about any smoked or grilled meat, including burgers, hot dogs and steaks, but you can also serve them on their own, as a tasty appetizer or side dish.
Soak wood chips in a large bowl of water for at least 30 minutes. You can use any type of flavored wood you prefer, such as mesquite, cherry, oak and hickory.
Fill the water pan in the smoker with water where indicated and add the charcoal, lighting and bringing them to between 200 and 225 degrees Fahrenheit. Use the vents on the smoker to adjust the temperature. Add the soaked wood chips when the coals start to ashen.
Slice the very top and bottom off of large onions so that they can stand upright, using a sharp chef's knife. At this point you can either leave the onions whole, cut them into quarters, slice them into rings, core out the centers or you can make partial slices all around each onion so they open up like a blooming flower, depending on how you wish to use or serve the onions.
Cover the onions in olive oil and season with salt and pepper, to taste. You can also spread butter and smashed garlic all over the onion for added flavor or, if you cored the centers, you can stuff it with the butter and garlic.
Wrap the onions loosely in aluminum foil and place them on the center rack of your smoker. Let them roast for 1 to 2 hours, until the onions are very soft and have a strong, smoky fragrance.