Rinse the lentils under cold water until the water runs clear, then set aside.
Dice the onion, carrots, and celery into small, even pieces to ensure they cook evenly and become tender.
Mince the garlic cloves finely to release their aromatic oils and flavor.
In a skillet over medium heat, warm the olive oil until it shimmers and begins to gently bubble.
Add the diced onion, carrot, and celery to the skillet. Sauté for about 5–7 minutes until they soften slightly, become fragrant, and start to develop a light golden color. Stir occasionally to prevent sticking.
Add the minced garlic to the skillet and cook for an additional 30 seconds until fragrant, stirring constantly to avoid burning.
Transfer the sautéed vegetables and garlic to the crockpot. Add the rinsed lentils, vegetable broth, bay leaf, thyme, and a pinch of salt and pepper.
Set the crockpot to low and cook for 6–8 hours, or on high for 3–4 hours. During cooking, the lentils will soften and the flavors will meld into a rich, hearty broth.
Once the cooking time is up, turn off the crockpot. Remove and discard the bay leaf and thyme sprigs. For a creamier texture, mash some of the lentils with the back of a wooden spoon or use an immersion blender to gently blend part of the soup.
Stir in the lemon juice to brighten the earthy flavors, then taste and adjust seasoning with salt and pepper as needed.
Serve the soup hot, garnished with herbs or a drizzle of olive oil if desired. The finished dish should be thick, hearty, with a warm aroma and a slightly oozy, comforting texture.
