Pour oil or ghee into a dutch oven and place over medium-high heat.
Add sweet potatoes and sauté for 2 to 3 minutes. Stir in onions, garlic, ginger, and Serrano chile and continue to sauté for 4 to 5 minutes. Season with salt and pepper.
Stir in red lentils, cumin, coriander, turmeric, ginger, and fenugreek leaves and continue to cook for 4 to 5 minutes, until mixture becomes fragrant and slightly smoky in scent.
Add diced tomatoes and stock and bring mixture to a boil. Once mixture is boiling, cover and reduce heat to medium-low and simmer for 30 to 35 minutes or until lentils have softened and mixture has turned into a stew-like consistency. Season with salt and pepper and stir in cilantro.
Top with more cilantro and serve with a side of grilled naan or steamed basmati rice.
