Mix together oil, bourbon, cider and seasoning packet.

Clean mushrooms and marinate for 30 minutes.

Cut your onion to the same thickness (or less) than your Portabella Mushroom, one per burger. Pre-heat your grill for direct heat grilling.

Drain mushrooms and place mushrooms and onion slices on grill.

Grill on one side for 3 – 4 minutes and then flip. Watch out for flare-ups! The brandy in the marinade will catch on fire but burns off very quickly.

Add slice of Provolone cheese to each mushroom to melt.

Toast hamburger buns.

Top it all off with some fresh sliced avocado and you are ready to devour this tasty morsel!