Start by rinsing the lentils under cold water until the water runs clear, then set aside.
Heat a large heavy-bottomed pot over medium heat, then add the olive oil, allowing it to warm up until it shimmers.
Add the minced garlic and ground turmeric to the oil, stirring constantly for about 1-2 minutes until fragrant and slightly golden, filling the kitchen with warm, spicy aroma.
Next, stir in the chopped carrots and celery, cooking for about 5-7 minutes until they start to soften and release their natural sweetness, and the vegetables look slightly glazed.
Pour in the vegetable broth and add the rinsed lentils, stirring gently to combine everything evenly.
Bring the mixture to a gentle simmer, then reduce the heat to low and let it cook uncovered for about 25-30 minutes, stirring occasionally, until the lentils are tender and beginning to break down, creating a creamy texture.
About five minutes before the end of cooking, stir in the chopped spinach and cook just until wilted and vibrant in color, which should only take a few minutes.
Turn off the heat and squeeze fresh lemon juice into the soup, stirring to brighten the flavors. Taste and season with salt and pepper as needed.
Ladle the hot soup into bowls, optionally garnishing with a drizzle of olive oil or fresh herbs if desired, and serve immediately to enjoy its comforting warmth and vibrant aroma.