Rijsttafel -- is there any way to avoid this on the Heart Of Belgium and Holland tour?

I haven't taken the tour but as a fellow food-allergy traveler, just opt-out of the meal and meet up with the people later. I wouldn't worry about a voucher for a meal - it's just one of those little things that costs you a little money but is totally worth it in the long run.

Eating at an Indonesian rijsttafel in Amsterdam is the only place I've ever had any reaction to food. I figured it was an overdose of MSG as I have no problem with peanuts. It is wonderful food for someone without any food allergies.
I understand how you have to be overly careful about food allergies, however.

Call the tour office and ask them. They'll want to know about the allergy anyway.

Mike, certainly talk to the RS staff about this in advance, and your guide first thing. I don't know where this meal takes place, but I imagine there is a way to arrange alternative dishes. RS in general, their guides in particular, and generally European restaurants are very ready for and attentive to special dietary limitations.

Mike,
We did the tour earlier this year. As the waiter brought the various items to the table he indicated which ones were peanut based. However it was several different small plates or bowls which were then passed family style, so frankly it was difficult to keep up with which were which.

Talk to your guide at the start of the trip, since this may be an issue at other meals and they will certainly work to avoid problems. My wife has shellfish issues and alternative meal choices have always been arranged. That said, if you have worries, you can always opt-out of any meal or activity. I do not know if a voucher would be provided.