Whisk all marinade ingredients together. Place in a large container or zip-top bag. Slice pork tenderloin into 1-inch thick slices. Place in the marinade and refrigerate about 30 minutes. Soak skewers in water while pork is marinating.
Heat grill to medium-high heat. I use the gas grill because it’s quicker.
Cut pineapple into chunks: Cut off top and bottom, then cut vertically all the way around to remove the skin. Cut vertically into quarters, then cut each quarter vertically down the center to remove the core. Slice 2 quarters into 1-inch thick slices. Reserve remaining half of pineapple for another use.
Cut onion into chunks: Slice off top and bottom. Cut onion in half, and then cut each half into 1-inch pieces.
Thread everything onto skewers, alternating pork, pineapple, and onion pieces.
Carefully oil grill grates. Grill kabobs on medium-high heat, rotating so that all sides get cooked, until pork reaches an internal temperature of 145°F, about 10-15 minutes. Remove kabobs from grill and serve!
Use low sodium tamari instead of soy sauce for gluten-free.