This is easy for me, as I normally do not eat lunch during the day when at home/working. I tend to eat a small snack once in a while. So I do the same when hiking.
The exception for when working is that if the day is stressful (of course goal is to eliminate stress in life), then I will take a lunch break... but the intent is to relieve stress, so I may run, walk, or even go the the gym. And I may sit down and eat a meal.
The exception for backpacking is that if I have a very hard section of hiking (i.e. huge elevation gain, extremely hot conditions, etc.), then I may take a "lunch" break. This could be at 10:00 AM, Noon, 2:00 PM, etc. Again it is to relax, re-coup, etc., not to eat a meal... but I often do eat a meal, but almost never cook something unless it is a cold, freezing, winter day.