Well, I have heard that working out first thing in the morning is the most effective as you burn up what you have already laid down as fat, rather than available energy from foods you have just consumed. Plus immediately after exercise you are still in fat burning mode, hence why many people consume protein shakes after a workout to replenish themselves. Therefore I would imagine that as long as there has been a large enough interval between your last meal and your walk (at least 2 hours) then walking before dinner would be the most effective option. But maybe check out the empirical evidence from studies of this nature yourself, just to be sure.
