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1
Preheat the oven to 350F.
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2
Place the lentils in a small saucepan, and cover with water by 1 inch.
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3
Bring to a boil; reduce to a simmer.
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4
Cover, and cook until the lentils are tender but still holding their shape, 15 to 20 minutes.
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5
Drain well and cool.
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6
Meanwhile, spread the walnuts on a baking sheet, and toast in the oven until fragrant and darkened, about 10 minutes.
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7
Let cool.
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8
In a food processor, combine the walnuts, breadcrumbs, garlic, cumin, coriander, red pepper flakes, 1 1/2 teaspoons salt, and 1/4 teaspoon pepper; process until finely ground.
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9
Add the lentils and 1 tablespoon of the oil; pulse until coarsely chopped (some lentils should remain whole).
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10
In a large bowl, whisk the egg.
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11
Add the lentil mixture; mix well.
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12
Divide into 4 equal-size parts; roll into balls, and flatten with the palm of your hand into 3/4-inch-thick patties.
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13
Heat the remaining 3 tablespoons oil in a large nonstick skillet.
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14
Add the burgers; cook over medium-low heat until crisp and browned, turning gently with a thin-edged spatula, 8 to 10 minutes per side.
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15
Transfer to a paper-towel-lined plate to drain.
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16
Serve with yogurt-cilantro sauce, if desired.
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17
In a small bowl, whisk together the yogurt, cilantro, and lemon juice; season with salt and pepper.
