Step 1

Add the cumin, mustard, and fennel seeds to a small sauté pan, and place on the stove over low heat. Toast the seeds, using a wooden spoon to stir frequently, until fragrant, 3 to 4 minutes.

Step 2

Add the toasted spices, lentils, water, tomatoes, onion, ginger, turmeric, salt, and pepper in the bowl of a 6-quart slow cooker. Stir together. Cover the slow cooker with the lid, then set to low and cook for 4 to 6 hours, or high and cook for 2 to 3 hours, until most of the liquid has been absorbed and the lentils are soft. Stir before serving.