Place pretzels in a large zip-lock bag and smash them with a meat tenderizer. Place in a bowl and set aside.
Combine all ingredients, except for crushed pretzels and sliced onion, in a large mixing bowl and mix until completely combined.
Preheat oven to 350 and lightly grease an baking pan (or an oven-safe skillet).
Form meatballs that are about 1 1/2 inches and roll each meatball in crushed pretzel. Press lightly and place them in a baking dish or an oven-safe skillet. Scatter sliced onions in between meatballs.
Bake for 30-35 minutes (depending on the size of meatballs).
Great pairing for these meatballs would be some mustard roasted potatoes. Just toss cut potatoes in a little bit of Grey Poupon mustard, salt, pepper and brown sugar and roast in the oven. (You can check this recipe for reference.)