In a large soup pot, heat the olive oil over medium heat. Add the chopped onion and carrots. Sauté for about 3 minutes until the vegetables begin to soften. Add in mushrooms and cook for another ~ 2 minutes until cooked down slightly.
Add the minced garlic, fresh thyme leaves, ground cumin, smoked paprika, and ground turmeric to the pot. Cook for another 1-2 minutes until the spices become fragrant.
Add the rinsed lentils and barley to the pot, followed by the vegetable broth, diced tomatoes, and bay leaves. Stir well to combine.
Bring the soup to a boil, then reduce the heat to low. Cover the pot and let the soup simmer for about 30-40 minutes, or until the lentils and barley are tender. Stir occasionally to prevent sticking.
Once the lentils and barley are cooked, remove the bay leaves. Season the soup with salt and pepper to taste.
Stir in the freshly squeezed lemon juice for a bright and zesty flavor.
Serve hot, garnished with fresh parsley or cilantro if desired.