Heat olive oil in a large pot over medium heat. Add onions, carrots, and celery. Sauté for about 5 minutes until the vegetables start to soften.
Stir in minced garlic and sliced mushrooms. Cook for another 5 minutes until mushrooms release their moisture and start to brown.
Stir in tomato paste, dried thyme, and smoked paprika. Cook for about 1 minute to let those flavors meld together.
Add lentils, diced tomatoes, vegetable broth, and bay leaf into the pot. Bring to a boil; then reduce heat and let simmer for about 25–30 minutes until lentils are tender.
Once lentils are cooked through, season with salt and pepper to taste. Add greens like kale or spinach and cook for an additional 5 minutes until they wilt down nicely.
Remove the bay leaf before serving. Garnish with fresh parsley if desired.