I served platters of green peppers, onions, and lettuce by a meal with bagels and salads which also had Milchig (cream cheese and cheese). I requested not to use the same utensils as the Milchig with everything else, but I don’t think people were careful about it. Can I wash the vegetables and cook them together with hot Fleishigs? They were cut with a Pareve knife and I put oil and salt on the onions before leaving them overnight.
If you make sure to wash them well so that there is definitely no Milchigs whatsoever on the vegetables, then it is OK.