Cut all the meat into 1" cubes. Toss with salt. Cover and refrigerate overnight.
Grind the meats together with half of the grated onion using a fine- to medium-fine plate. Pass it through twice for a smooth texture.
Mix the remaining grated onion, the garlic, paprika, pepper, and any remaining salt.
Mix baking soda into sparkling water, then knead into the meat until it becomes stick and cohesive (3-5 minutes).
Cover and refrigerate again for 8-24 hours.
With wet hands, form into small sausage cylinders.
Grill over medium high heat, using good lump charcoal (like Royal Oak) if possible. Cook until golden brown... don't overcook!
Serve stuffed into somun or pita bread. Top with sliced raw onion and ajvar.