SL, I most agree except: is is healthy to consume a fiberous veggie pre-workout (simple because they are all healthy), but apart from any potential alkalinity buffer which they may afford (and this is wildly speculative), I don't think its necessary.
What you want is good carbs and protein and minimal stomach bloat during the workout.
Oatmeal, sweet potato, beans, etc are already low GI - they will provide you with good energy intra-workout - you already have a protein source to further delay the carb release, you don't further need spinach or something like that.
Also remember glycogen is stored. Getting pre-workout carbs is more critical AM (when your glycogen depleted) than at other times.
I would however do as SL suggest and consume them at any time, maybe less PM if I had consumed plenty of carbs already.