Heat olive oil in a large heavy-bottomed pot over medium heat until it shimmers and begins to gently sizzle.
Add the chopped onion and a pinch of salt. Cook, stirring occasionally, until the onion becomes translucent and starts to caramelize around the edges, about 5 minutes. You’ll smell a sweet aroma as it softens.
Stir in the minced garlic and grated ginger, cooking for about 1 minute until fragrant. The mixture should emit a warm, spicy aroma, and the garlic will turn golden at the edges.
Add ground turmeric and cumin, stirring constantly for about 30 seconds to toast the spices and release their aromas. The spices will turn a deeper yellow and smell warm and earthy.
Pour in the vegetable broth, bringing the mixture to a gentle simmer, and add the rinsed red lentils. Stir well to combine, then cover the pot partially and let it simmer for about 20 minutes, stirring occasionally, until the lentils are soft and breaking down.
Add the diced carrots and continue simmering uncovered for another 10 minutes until the carrots are tender and the soup has thickened into a velvety consistency. Stir occasionally to prevent sticking at the bottom.
Stir in the chopped spinach or kale, cooking just until wilted, about 2-3 minutes. Taste the soup and adjust seasoning with salt as needed.
Squeeze in fresh lemon juice to brighten the flavors. Give the soup a final stir, taste again, and adjust salt or acidity as desired.
Remove the soup from heat and let it sit for a few minutes to allow flavors to meld. Serve hot, garnished with a drizzle of olive oil or fresh herbs if desired.
