Heat olive oil in a large pot over medium heat. Add onion and garlic and cook until softened, about 5 minutes.
Add vegetable broth, diced tomatoes, carrots, celery, sweet potato, and red lentils. Bring to a boil, then reduce heat and simmer for 20 minutes, or until vegetables are tender.
Stir in spinach, kale, turmeric, ginger, and black pepper. Cook for another 5 minutes.
Remove from heat and stir in lemon juice. Season with salt and pepper to taste.