Trader Joe diced yellow onions

In general are all raw, precut onions (no certification) ok for Passover? Is there any difference with frozen vegetables?

Thank you!

Yes they are fine.

Frozen vegetables; as long as only vegetables are listed in the ingredients they do not need further checking. Albeit if they are vegetable that don’t have an insect infestation issue otherwise they would require a Reliable expert certification. (for example leafy vegetables, broccoli, cauliflower, etc. do )