Step 1: Sauté Aromatics : Heat 1 tablespoon olive oil in a large pot. Add chopped onion and minced garlic. Cook over medium heat until onions are soft and translucent, about 3–4 minutes.
Step 2: Cook Vegetables : Add diced carrots, celery, zucchini, and bell pepper. Stir and cook for 3–4 minutes until slightly softened.
Step 3: Add Spices : Sprinkle in cumin, smoked paprika, thyme, black pepper, and optional chili flakes. Stir to coat vegetables with the spices.
Step 4: Add Lentils and Liquid : Pour in rinsed lentils, diced tomatoes, and vegetable broth. Stir well. Bring mixture to a boil.
Step 5: Simmer : Reduce heat to low, cover, and simmer for 30 minutes or until lentils are tender. Stir occasionally.
Step 6: Add Greens : Add chopped spinach or kale. Cook for 5 more minutes until greens are wilted. Adjust salt and add lemon juice if desired.
Step 7: Serve and Garnish : Ladle soup into bowls. Garnish with chopped parsley and a drizzle of olive oil. Serve with crusty bread.