Saute the onion in vegetable broth until tender and translucent.
Add garlic, cumin, black pepper, cardamom, cayenne (½ tsp if you like it spicy), cinnamon stick, curry powder, and salt. Saute until the spices bloom and become fragrant.
Add tomato sauce, sweet potatoes, coconut milk, broth, chili pepper, and lentils to the pot and mix well.
Increase the heat to high and bring to a boil, then reduce heat to low and let simmer, uncovered, for 15-20 minutes or until the lentils are tender and cooked through.
Remove the cinnamon stick before serving.
Ladle the stew into bowl(s) on top of a bed of spinach; the residual heat of the stew will soften the spinach.
Garnish each bowl with lime juice and a spoonful of Cilantro Lime Chutney - serve warm.