Fillings for Onigiri- Freezer/Meal Prep Friendly

Looking for suggestions and anecdotes on what fillings freeze well for meal prepped onigiri that I will eat within the week. I have found so far that wrapping them still warm and thawing at room temp which should probably be a consideration. Also curious if there is a better way to do this as far as thawing and storing if I'm going to make a batch ahead of time. Thanks!