I started with one of the heaviest ingredients, the raspberry sauce. I put about a teaspoon on the bottom of the cap:

And a teaspoon directly into the bowl, and spread it around the top of the cap:

Next, pour orange juice into the bowl. I put around 1/3 of a cup in:

Followed by 2 tablespoons of the light soy sauce and teriyaki sauce. Then, add about 1 teaspoon of the extra virgin olive oil:

Honey

Add honey.

Be sure to put a large daub on the bottom of the cap also:

Remove the cap and place it in a freezer-thick baggie. Take a fork and mix up the remaining marinade:

Add the marinade to the baggie, and slosh it around so it covers the bottom of the cap evenly.

Try to arrange it in the fridge so the marinade is absorbed by as much of the cap as possible. Let the marinade sit for a few hours. Basically the longer it sits, the more flavor will infuse into the cap. Be sure to rotate the bag so the marinade is distributed evenly.

Hooray! Now that you feel your cap has marinated long enough, remove it from its bag and place it in a frying pan on medium heat. Add about 1-2 tablespoons of the marinade to the pan for something for the cap to heat up in. Slice your onion and put a few of the slices into the frying pan along with the cap.

Start preparing your bun.

Cut a slice or two of tomato to put on the bun.

Put your fixins' on the bun. Ketchup, mustard, relish, tomato, nayonaise, and carefully take the fried onions out of the pan and put 'em on the bun:

Cut a thin slice of vegan cheese and place it on the cap in the pan. Once you feel the cheese is sufficiently heated up, take the cap and cheese and add them to the bun:

Add the slightest pinch of fresh ground pepper to the cap, only enough to taste, and top with spinach:

Now that you have learned how to make vegan marinated portobello mushroom burger, please be sure to view these other burgers recipes.