Do I have a scientific explanation about how the marinade breaks down the cellulose structure of the vegetable cells and penetrates each with vital flavor? No. All I know is I've been doing it for a few years and it tastes good to me. What? That's not good enough? You want PROOF? Okay.
Here is a bowl of veggies to be grilled, WITHOUT MARINADE. Notice how they all are reserved and shy, keeping their flavors separate? It's like boys and girls at the first school dance. No mingling of tastes.


Southwest-ish Veggie Marinade
(I just actually named it for the first time one sentence ago...aren't you proud?)
2 T vegetable oil
3 T lime or lemon juice
1/2 t kosher salt
1/2 t black pepper
1/2 t chili powder
1/2 t cumin
Slowly pour oil into the juice while you whisk feverishly like a madman. (A bit over dramatic?) Add spices. Toss veggies in the mix, marinade for 30-60 minutes, and grill.
If I'm doing stir fry, I do a similar thing:
Asian-ish Veggie Marinade
1.5 T peanut oil
1/2 T sesame oil
3 T rice wine vinegar
1/2 t garlic powder, fresh ground from dried minced garlic
1/2 t ginger, fresh ground
1/2 t basil, fresh chopped
1/4 t red pepper flakes
Thank goodness I don't have an Amish veggie marinade because "Amish-ish Veggie Marinade" would sound silly.