What you're asking is a little bit outside my area of expertise, but in the absence of any other input I'll share a few thoughts in case it helps - note that this is from my own quick scan of a few regs, rather than any specific familiarity with this type of product/situation.
"Ready to cook" is perhaps going trigger an obligation for you under Article 9(1)(j) of Regulation (EU) 1169/2011: ...indication of the following particulars shall be mandatory: (j) instructions for use where it would be difficult to make appropriate use of the food in the absence of such instructions.
Whether it's actually going to be "difficult" to make use of the food will depend on exactly what it is, but I'm assuming it'll be not dissimilar in principle to the bags of stir fry vegetable mixes one finds in supermarkets? In which case these usually have cooking instructions and sometimes an indication that the product is unsuitable to eat raw, along with e.g. "straight to wok" or similar that is broadly equivalent to your planned "ready to cook" statement.
It can sometimes be useful to look at labels for existing products, particularly where they owned by brands/retailers with large and (generally) competent technical/regulatory teams, so a bit of a factfinding mission in your local supermarket can sometimes be surprisingly beneficial 
Obviously you'd need to validate the cooking instructions, to ensure that following them does actually give a final product that is safe for RTE.
It's not a process I've used so can't say for sure, but there is scope for using various things in the washing process that are then non-declarable if they are genuinely only carried over from use as processing aids - see Article 20(b)(i) and also potentially Article 20(d) of Regulation (EU) 1169/2011.
In my limited experience it's also the case that the retailers are pretty thorough on wash performance and validation thereof, so if that's the target you've set then I'd be looking at this part of your process very thoroughly.
