In a large pot, heat the olive oil over medium heat. Add the diced onion and garlic, and sauté until fragrant and translucent, about 3-4 minutes.
Stir in the carrots, celery, sweet potato, and butternut squash. Cook for an additional 5-7 minutes, allowing the vegetables to soften slightly.
Add the chickpeas and vegetable broth to the pot. Bring the mixture to a boil, then reduce the heat and let it simmer for 20-25 minutes, or until all vegetables are tender.
Stir in the chopped kale, thyme, rosemary, salt, and pepper. Simmer for an additional 5 minutes until the greens are wilted and tender.
Just before serving, stir in the lemon juice and adjust seasoning to taste. If desired, sprinkle with red pepper flakes for an extra kick.
Ladle the soup into bowls and enjoy!