In a large pot or Dutch oven, combine the red lentils, vegetable broth, and 4 cups (960 ml) of water.
Bring to a simmer over medium-high heat.
Skim off any foam that rises to the surface.
Reduce the heat to medium-low, cover the pot, and let it simmer for 5 minutes, stirring occasionally.
Add the chopped onion, celery, carrots, and minced garlic to the pot.
Stir to combine and continue to simmer, uncovered, for 20 minutes.
Stir in the chopped cilantro, curry powder, and ground cumin.
Continue cooking for another 20 minutes, or until the lentils are completely soft and have started to break down.
Remove the pot from the heat.
Stir in the fresh lemon juice and season with salt and pepper to your liking.
Serve hot, garnished with extra cilantro if desired.
Garnish with a swirl of coconut yogurt, a sprinkle of fresh cilantro, or a squeeze of lime to brighten the flavors just before serving.