Heat a large saucepan or Dutch oven over medium heat. Melt coconut oil and sauté sweet potatoes, butternut squash, carrots, and onions for 5 to 7 minutes. Add garlic during the last 1 minute of cooking, so it doesn’t burn.
Place all vegetables back to the pot and stir in ginger, curry powder, tomato paste, coconut milk, vinegar, serrano (if using), and kale or spinach. Reduce heat to a simmer. Stirring occasionally, cook for 20 minutes, until vegetables are tender.