Heat a large heavy-bottomed pot over medium heat and add a tablespoon of oil. Once shimmering, add the cumin seeds and toast for about 30 seconds until fragrant.
Add the finely chopped onion to the pot. Sauté for about 5 minutes, stirring often, until it turns translucent and begins to smell sweet.
Stir in the diced carrots and celery. Cook for another 5-7 minutes, stirring occasionally, until the vegetables soften and release their aroma.
Add the grated fresh ginger and ground turmeric. Stir well and cook for 1-2 minutes until the spices release a warm, smoky aroma, watching for a slight sizzle.
Pour in the vegetable stock and bring the mixture to a gentle simmer. Add the rinsed lentils and stir to combine.
Cover the pot partly and let the soup simmer for 25-30 minutes, until the lentils are tender and the vegetables are soft. Stir occasionally and listen for gentle bubbling.
Add the chopped greens to the pot in the last 5 minutes of cooking. Let them wilt and turn vibrant green, adding a fresh aroma and slight bitterness.
Taste the soup and adjust the seasoning with salt, pepper, and a squeeze of lemon juice for brightness. Use an immersion blender to puree part or all of the soup if you prefer a creamier texture.
Remove from heat and let sit for a few minutes to deepen the flavors. Serve hot, garnished with a drizzle of olive oil or fresh herbs if desired.
