Well, I don't know what the 'right' way is of making them, but this is what I put in:

Egg - for binding
Bread crumbs - enough to get right consistency - not too wet
I would probably use the soup mix - dependent on how much mince you might only want half as it will be too salty
Onion finely diced
couple tablespoons tomato sauce

I also put finely grated carrot and zucchini in mine but you don't have too.