1 cup lentils
2 cups water
2 cloves garlic, coarsely chopped
1/2 medium yellow onion, coarsely chopped
1 1/2 teaspoons fine salt, divided
8 ounces brown mushrooms, quartered
1/2 cup rolled oats (not instant)
2 tablespoons ground flaxseed meal
2 tablespoons maple syrup
1 teaspoon dried sage
1 teaspoon fennel seeds
1/4 teaspoon freshly ground black pepper
4 tablespoons olive oil
Rinse the lentils. Bring the water to a boil in a small saucepan over medium-high heat. Add the lentils, garlic, onion, and 1/4 teaspoon of the salt, and stir to combine. Reduce the heat to medium-low and simmer uncovered, stirring occasionally, until the lentils are tender, 20 to 30 minutes.
Meanwhile, place the mushrooms in a food processor fitted with the blade attachment and pulse until finely chopped, about 5 (1-second pulses). Add the oats, flaxseed, maple syrup, sage, fennel, and remaining 1 1/4 teaspoons salt to the food processor and set aside until the lentils are ready.
Drain the lentil mixture to remove any excess water, then add the drained mixture to the food processor. Pulse into a coarse paste, about 10 (1-second) pulses. Form into 20 (2-inch-wide) patties (about 2 tablespoons each).
Heat 2 tablespoons of the oil in a large nonstick frying pan over medium heat until shimmering. Add 1/3 of the patties and cook until browned, about 3 minutes per side (be careful when flipping and use a flat spatula; they are delicate). Remove to a serving plate. Repeat frying the remaining patties, adding a tablespoon of oil between each batch.