Rinse the red lentils thoroughly under cold water until the water runs clear.
In a medium pot, combine lentils and 3 cups of vegetable broth or water. Bring to a boil, then reduce heat to a simmer. Cook uncovered for about 15-20 minutes, stirring occasionally, until the lentils are soft and starting to break down.
While the lentils are cooking, heat the oil in a large pan over medium heat.
Add the cumin seeds and mustard seeds. Once they start popping, add the chopped onions. Sauté until the onions are golden brown (about 5-7 minutes).
Add the garlic, ginger, and green chilies, and cook for another 1-2 minutes until fragrant.
Stir in the turmeric, ground cumin, ground coriander, and garam masala. Cook for 30-60 seconds to toast the spices.
Add the chopped tomatoes to the spice mixture and cook for 4-5 minutes until they break down and release their juices.
Pour the cooked lentils into the pan with the tomato and spice mixture. Stir well to combine. If the dal is too thick, add a bit more vegetable broth or water to reach your desired consistency.
Simmer everything together for 5-10 minutes, allowing the flavors to meld. Season with salt to taste.
Remove the dal from heat. Garnish with fresh cilantro, a squeeze of lemon or lime and some vegan cream or vegan yogurt if desired.
Serve hot with rice, naan, or other flatbread.
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Notes
Refrigerator: Store leftover dal in an airtight container in the refrigerator for up to 4 days.
Freezer: Transfer the red lentil dal to a freezer-safe container or freezer bag. It will keep well for up to 3 months; thaw in the refrigerator before reheating.
To reheat: Reheat on the stovetop or in the microwave until warmed through, adding a splash of water or broth if the dal is too thick.