Wash and drain the lentils if you haven’t yet. Chop up the veggies. Chop them any way if you plan to purée the soup( uneven chunks will work fine as they are going to get puréed), chop them evenly and small , if the soup won’t be puréed

Heat a saucepan or deep skillet over medium heat and add the oil. Once the oil is hot, add the onion and a good pinch of salt. Cook for about 3 minutes, until the onion starts to turn translucent. Mix the ginger and garlic, and cook for about a minute.

Add the carrots and celery along with another pinch of salt. You can add more vegetables at this point, as well, if you like. Mix well, cover with a lid, and cook for about 2 minutes. (Cooking the carrots and celery first ensures they soften properly, especially if they are chopped into larger pieces. If using whole lentils instead of split red lentils, you can skip this step and add them when you add the lentils, since those have a longer cooking time.)

Open the lid, and add the paprika, balsamic vinegar, and black pepper. Mix well, then add the tomatoes, water, washed lentils, and remaining salt. Mix well, then cover and cook for about 10 minutes. Open the lid, stir well, and continue cooking for another 3 to 4 minutes. Check if the lentils are done to your preference. If they need more time, continue cooking until they are tender.

If the soup has thickened too much, adjust the consistency by adding more water or stock. You can now either puree some or all of the soup, or mash some of the lentils with a spatula, so the soup becomes creamy but still has a little bit of texture. If pureeing, switch off the heat, let the soup cool slightly, then blend in batches before putting it back into the pan. Or use an immersion blender to blend.

Now, fold in the spinach and some lemon juice, and adjust the consistency again, if needed, with more stock. If you want the soup creamier, stir in the optional non-dairy yogurt. Cover and let the spinach cook for another 1 to 2 minutes. Taste and adjust the salt, spice, or herbs as needed. Serve the soup in bowls and top with pepper flakes, cilantro or green onion, and sambal oelek or hot sauce. You can also top it with crispy lentils, smoky tofu crumbles, croutons, or toasted bread.