Sauté the Foundation: In a large Dutch oven over medium heat, warm the 3 tablespoons of olive oil. Once shimmering, add the chopped onion, carrots, and celery. Sauté, stirring occasionally, for 8-10 minutes until the vegetables have softened significantly and the onion is translucent. This slow sauté builds a sweet, flavorful base.
Bloom the Spices: Add the minced garlic, smoked paprika, cumin, and coriander to the pot. Stir constantly for 45 seconds until the spices are intensely fragrant. This toasting step unlocks their essential oils.
Intensify the Tomatoes: Pour in the can of diced tomatoes and the balsamic vinegar. Increase the heat slightly and cook for 3-4 minutes, stirring and scraping the bottom of the pot to release any flavorful bits. The tomatoes will darken slightly and their flavor will concentrate.
Simmer and Infuse: Add the rinsed lentils, rinsed pearl barley, unsalted vegetable broth, dried shiitake mushroom, black pepper, and red pepper flakes. Stir to combine. Increase the heat to high and bring the soup to a boil. Once boiling, reduce the heat to low, cover the pot partially, and maintain a gentle simmer for 35-40 minutes, or until both the lentils and barley are tender.
Create a Creamy Texture: Remove the pot from the heat. Discard the shiitake mushroom (or bay leaf). Using an immersion blender, pulse the soup 5-7 times directly in the pot. Your goal is not a smooth purée, but a creamy base that still has plenty of whole lentils and barley for texture. If using a standard blender, carefully transfer about one-third of the soup, blend until smooth, and return it to the pot.
Wilt and Brighten: Stir the chopped kale and fresh parsley into the hot soup. The residual heat will wilt the greens perfectly in about 2-3 minutes, preserving their vibrant color and nutrients. Finally, stir in the 2 tablespoons of lemon juice.
Serve: Taste the soup and add more black pepper or red pepper flakes if desired. Ladle into warm bowls and finish with a generous drizzle of high-quality extra virgin olive oil.