Dice all vegetables and rinse lentils.
Heat olive oil in a large pot; sauté onion and garlic.
Add carrots, squash, and celery; cook until slightly softened.
Add spices: cumin, smoked paprika, chili flakes, turmeric, salt, and pepper.
Stir in lentils, diced tomatoes, and vegetable broth.
Bring to a boil, then simmer for 25–30 minutes.
Add kale or spinach and cook until wilted.
Taste and adjust seasoning. Add lemon juice if desired.
Serve hot with optional garnishes.