Start by chopping the onion, carrots, and celery into small, even pieces. Set them aside.
Heat a large heavy-bottomed pot over medium heat and add a drizzle of olive oil. When shimmering, add the chopped onion and cook until translucent, about 5 minutes, until it becomes fragrant and slightly golden.
Add the diced carrots and celery to the pot. Sauté for another 3-4 minutes until the vegetables start to soften and smell sweet.
Stir in the minced garlic and cook for 30 seconds until fragrant, being careful not to burn it.
Add the rinsed lentils to the pot, stirring to coat them with the aromatic vegetables. Let them toast for a minute, releasing their earthy aroma.
Pour in the vegetable broth, bringing the mixture to a gentle boil. Once bubbling, reduce the heat to low, cover the pot, and let it simmer for about 25-30 minutes, or until the lentils are tender and the vegetables are cooked through.
Add the diced tomatoes, cumin, thyme, and smoked paprika. Stir well, then continue simmering uncovered for another 5 minutes to allow the flavors to meld.
Taste the soup and adjust the seasoning with salt and pepper. If you prefer a smoother texture, use an immersion blender to blend part of the soup directly in the pot until creamy, leaving some lentils intact for texture.
Finish by stirring in a squeeze of lemon juice for brightness and sprinkle with freshly chopped parsley or cilantro for freshness.
Serve the hot lentil vegetable soup in bowls, enjoying the hearty, thick texture and the comforting aroma. Pair with crusty bread or enjoy as is for a wholesome meal.
