Heat a tablespoon of olive oil in a large pot over medium heat until shimmering and fragrant.
Add the chopped onion, carrots, and celery to the pot. Cook, stirring occasionally, until the vegetables soften and smell sweet, about 8 minutes.
Stir in the minced garlic and grated ginger. Cook for about 1 minute until fragrant, making sure not to burn the garlic.
Add the turmeric and cumin powders, stirring well to coat the vegetables. The mixture will turn a vibrant yellow and release warm aromas.
Pour in the vegetable broth and bring the mixture to a gentle simmer. Add the rinsed lentils, stirring to combine.
Let the soup simmer uncovered for 25-30 minutes, stirring occasionally, until the lentils are tender and the soup has thickened slightly.
Add the chopped spinach or kale during the last 5 minutes of cooking. Stir until wilted and vibrant in color.
Season the soup with salt and pepper to taste. For brightness, add a squeeze of lemon juice or sprinkle fresh herbs if desired.
Use an immersion blender to partially blend the soup if you prefer a creamier texture, leaving some chunks for texture.
Remove the pot from heat and let the soup rest for a few minutes. Serve hot, garnished with extra herbs or a drizzle of olive oil for a cozy presentation.