Prepare the Mushroom Patty:

1. Clean the mushrooms by gently wiping them with a damp cloth to remove any dirt. Avoid soaking them in water, as mushrooms are like sponges and will absorb too much liquid.
2. Slice or chop the mushrooms finely, depending on your preferred texture. Finely chopped mushrooms will provide a more uniform patty.
3. Heat a large skillet over medium-high heat and add the olive oil. Once hot, add the minced garlic and shallot, sautéing for 2-3 minutes until they become fragrant.
4. Add the sliced mushrooms to the skillet. Cook and stir frequently until the mushrooms release their moisture and turn golden brown, about 8-10 minutes. This step intensifies their flavor and removes excess moisture.
5. Season the mushrooms with fresh thyme leaves, salt, and pepper. Stir to incorporate the seasonings evenly.
6. Transfer the cooked mushrooms to a bowl and let them cool slightly. Once cooled, add the breadcrumbs and beaten egg to the mushroom mixture. Mix thoroughly until you have a cohesive mixture that holds together when shaped into patties. If the mixture is too wet, add more breadcrumbs.

Shape and Cook the Patty:

1. Divide the mushroom mixture into four equal portions. Shape each portion into a patty, roughly the same size as your burger buns.
2. Heat the same skillet over medium-high heat and add a bit more olive oil if needed. Place the mushroom patties in the skillet and cook for about 3-4 minutes per side, or until they are nicely browned and have a crispy exterior.
3. During the last minute of cooking, place a slice of Swiss cheese on top of each patty and cover the skillet with a lid to melt the cheese.

Assemble the Mushroom Marvel Burger:

1. Toast the burger buns lightly until they are golden brown.
2. Spread your preferred condiments on the bottom half of each bun.
3. Place a lettuce leaf on top of the condiments, followed by the mushroom patty with melted cheese.
4. Add sliced tomatoes, red onions, and avocado (if using) on top of the patty.
5. Complete the burger with the top half of the bun.
6. Serve your Mushroom Marvel Burger with optional pickles and your choice of side dishes.