Pulse the onion in a food processor until finely chopped and pulpy. Using a silicone spatula scrape the onion into a sieve, use the spatula to press any juices out of the onion, then transfer the onion to a large mixing bowl
Add everything but the butter to the bowl.
Vigorously knead the meat for 5 minutes. It should be tacky and easily hold together when picked up.
Tightly roll the meat into 10 equal sized balls (around 115g each)
Take each ball and press it into the center of a flat skewer then roll the meat between your palms to form a log 2" thick
Kabobs are usually done over coals, but to do them inside heat a cast iron griddle over medium-high heat until sizzling, add the kabobs and cook 5-8 minutes per side until nicely browned and around 165F internal temp
Just before serving, brush the kabobs with melted butter