You can use any meat filling recipe you like to stuff them. I made a take on a Turkish ground lamb mixture to stuff green peppers from the garden. I think it was something like ground lamb, minced onion and garlic, dried mint and oregano, sumac, S&P. Not sure what else I may have added. You can find recipes for kofte that are similar. Or you can use your frikadellar recipe.
We roasted some for dinner that night and froze some for a future dinner.
Anyplace where people argue about food is a good place.
~ Anthony Bourdain, Parts Unknown, 2018