Heat olive oil in a large pot over medium heat. Add diced onion and minced garlic, sautéing until fragrant and translucent, about 2-3 minutes.
Add diced carrot and cook for another 3-4 minutes until slightly softened and fragrant.
Stir in the turmeric powder and cook for 30 seconds to release its aroma.
Add the rinsed lentils, chopped tomatoes, and vegetable broth to the pot. Stir well to combine all ingredients.
Bring the mixture to a boil, then reduce heat to low and cover. Let it simmer gently for about 25-30 minutes, or until the lentils are tender and the soup has thickened.
Uncover the pot and stir in chopped spinach, cooking for another 2-3 minutes until wilted and vibrant green.
Season with salt and pepper to taste, adjusting flavors as needed.
Serve the soup hot, garnished with a drizzle of olive oil or fresh herbs if desired.