1 large onion, quartered through root end
2 bay leaves
1½ cups black beluga or French green lentils, rinsed, picked through
Kosher salt
¼ cup olive oil
1 teaspoon coriander seeds
½ teaspoon cumin seeds
3 tablespoons sherry vinegar or red wine vinegar
Freshly ground black pepper
6 radishes, trimmed, very thinly sliced
4 scallions, thinly sliced
1 cup parsley and/or mint leaves
1 cup thinly sliced celery hearts and leaves
Cook onion, bay leaves, and lentils in a large saucepan of simmering salted water until lentils are tender but still firm, 15–20 minutes. Drain; discard onion and bay leaves and transfer lentils to a medium bowl.
Heat oil in a small skillet over medium. Cook coriander seeds and cumin seeds, swirling skillet, until fragrant, about 1 minute. Add spice mixture and vinegar to lentils, season with salt and pepper, and toss to coat.
Just before serving, top lentils with radishes, scallions, herbs, and celery; season with salt and pepper.
Do Ahead: Lentils (without herbs and vegetables) can be marinated 3 days ahead. Cover and chill.
Calories (kcal) 400 Fat (g) 16 Saturated Fat (g) 2 Cholesterol (mg) 0 Carbohydrates (g) 53 Dietary Fiber (g) 14 Total Sugars (g) 4 Protein (g) 17 Sodium (mg) 60