Start with seasoning the mushrooms and zucchini. Place them in the mixing bowl with about a teaspoon of olive oil and a few dashes of your favourite dry rub. Toss/mix this up until the mushrooms are coated. Then blend in a food processor.
Portion into 6 balls to flatten into patties.
Before you start cooking the mushrooms and zucchini patties, get your onions going. The goal is to caramelize them. I mix about three ounces of water with about a tablespoon of agave syrup. You can use simple syrup or maple syrup as alternatives. Heat the pan with about a tablespoon of olive oil and add sliced onions, water, syrup, salt and pepper. Let them cook until they are translucent. This takes a while. So use low/medium heat.
Cook your veggies! Pre-heat your grill. I put on high heat and cook the veggies for about 3 minutes per side. Also, I always cook my veggies medium-rare.
I like to toast my buns on the grill while I am cooking my veggies. Another thing that you can do while the veggies are cooking is mash an avocado.
Now that your veggies are grilled, onions are caramelized, mashed avocado and buns are toasted – you can build your burger.