Rinse the lentils thoroughly under cold water until the water runs clear. If you have time, soak them for 15 minutes to help them cook faster and more evenly.
Heat the olive oil in a large pot over medium heat. Add the chopped onion and sauté until it becomes translucent and fragrant, about 5 minutes, with a gentle sizzle and a slight aroma filling the kitchen.
Add the minced garlic and ground turmeric to the pot. Stir constantly for about 30 seconds until the mixture releases a warm, earthy scent and the garlic becomes fragrant.
Introduce the chopped carrots, celery, and bell pepper into the pot. Sauté the vegetables, stirring occasionally, until they start to soften and release their natural sweetness, about 7 minutes. The vegetables should become slightly tender and the mixture will smell vibrant.
Drain the soaked lentils and add them to the pot. Stir well to coat the lentils with the spices and vegetables, allowing the flavors to meld for a minute or two.
Pour in the vegetable broth, and bring the mixture to a gentle boil over high heat. Once boiling, reduce the heat to low, cover the pot, and let it simmer gently for 25-30 minutes, or until the lentils are tender and the vegetables are soft. You should hear a gentle bubbling sound during simmering.
Check the seasoning and add salt and pepper to taste. Squeeze in fresh lemon juice to brighten the flavors. Adjust the seasoning as needed, tasting for balance between earthiness and acidity.
If you prefer a creamier texture, use an immersion blender directly in the pot to puree about half of the soup. Alternatively, transfer a portion to a blender, blend until smooth, then stir it back into the pot. The soup should become thick and velvety but still with some vegetable pieces remaining.
Remove the soup from heat and let it rest for about 5 minutes. The flavors will deepen and the texture will settle, making it even more comforting to serve.
Ladle the warm, golden soup into bowls. Garnish with fresh herbs if desired, or drizzle with a little extra olive oil for added richness. Serve hot, enjoying the aroma and creamy texture with each spoonful.