How to Make It
In a medium skillet, heat the olive oil over medium-high heat. Add the onion, garlic, and Serrano pepper until the onions have softened and lightly browned, about 5 minutes. Add the turmeric, mustard seeds, cumin, coriander, cinnamon, chili powder, and salt and cook for another 2 minutes. Transfer the spiced onion mixture to the slow cooker, followed by the lentils, and vegetable stock.
Cover and cook on high for 2 hours or on low for 4 hours, until the lentils have softened. In the final 20 minutes of cooking, turn the slow cooker to low heat and add the coconut milk and Swiss chard to combine. Cover and cook for 20 more minutes until soup is heated through and the chard is bright green and tender.
To serve, season to taste with salt and pepper. Add a dollop of Greek yogurt or crumbled cheese and garnish with chopped parsley.