Prep and measure out all of your ingredients and set them aside.
Preheat your oven to 375°F (190°C).
Heat a large skillet over medium heat for 2 minutes and then add the onions and cook for 5 minutes, stirring frequently and adding a splash of water when they start to stick or look dry.
Add the mushrooms, celery, garlic and green onion and cook for an additional 3 minutes. Turn off the heat and transfer the mixture from your skillet into your food processor, along with the cooked lentils and rolled oats. Pulse 10 - 15 times, until the mixture is coarsely mixed up.
Transfer the mixture from the food processor to a large mixing bowl and add the chia seeds, parsley, black pepper and salt. Stir the mixture until well combined and then form into 7 equal-sized patties and place on a parchment covered baking sheet.
Bake for 15 minutes and then flip, and bake for another 15 minutes on the other side.
Top with thinly sliced red onions, fresh tomatoes, lettuce, and plant based mayo when serving!
Follow this recipe for perfectly cooked lentils on the stove top or in your Instant Pot. This lentil recipe has seasonings, so just leave out the seasonings when making them for your burgers.