Prepare the lentils:

1. In a medium saucepan, combine the rinsed lentils and water (or broth) and bring to a boil. Reduce heat to low and cover. Simmer for about 25-30 minutes, or until the lentils are tender. Drain any excess liquid and set aside to cool slightly.

Make the burger patties:

1. Heat olive oil in a large skillet over medium heat. Add the chopped onion and garlic, and sauté for about 5 minutes, until softened.
2. Add the chopped mushrooms to the skillet and cook for 7-10 minutes, until the mushrooms release their moisture and become soft. Season with salt, pepper, cumin, paprika, and turmeric. Stir to combine and cook for another minute.
3. In a large mixing bowl, mash the cooked lentils with a fork or potato masher until mostly mashed, leaving some lentils intact for texture.
4. Add the mushroom-onion mixture to the mashed lentils, along with the breadcrumbs, soy sauce (or tamari), flax egg (or regular egg), and fresh herbs, if using. Stir until everything is well combined.
5. Taste the mixture and adjust the seasoning with more salt, pepper, or spices if necessary.
6. Form the mixture into 4-6 patties, depending on the size you prefer. If the mixture is too sticky, refrigerate it for 15 minutes to help it firm up.

Cook the patties:

1. Heat a small amount of olive oil or non-stick spray in a skillet over medium heat. Cook the patties for about 5-7 minutes on each side, until golden brown and crispy.
2. Alternatively, you can bake the patties at 375°F (190°C) for 20-25 minutes, flipping halfway through, until they are firm and golden.

Assemble the burgers:

1. Toast the burger buns (optional) and spread your choice of condiments (mustard, mayo, etc.) on the buns.
2. Place the lentil mushroom patties on the bottom buns and top with your favorite burger toppings, such as lettuce, tomato, onions, pickles, and cheese.
3. Serve immediately and enjoy!