The best way to find a journal is on Scimago (in my opinion).
You can search Journals by categories or research them by keywords (e.g., "Eating" or Eating disorder*).
For instance, here is a list of nutrition and dietetics journals: https://www.scimagojr.com/journalrank.php?category=2916&order=sjr&ord=desc
They are ranked according to their SJR (but you can change the rank according to their H-index if you prefer). If they are some APC, you will see a "lock" logo (the open-access logo). But note that some OA journals are free (so you better check the information in the authors' guidelines).
If you mean open access journals that grant article fee processing waiver, you could try BMC journals which has a journal for eating behavior. There are also journals of Frontiers in psychology and psychiatry that provide fee waiver. Of course, these waivers are for authors from low income countries. Though you can talk with them before submitting the manuscript.
Otherwise, you could consider the journals of articles you have cited in your paper.