Heat vegetable oil over medium heat in a large saucepan, add the onion and saute until transparent.
Add the garlic and ginger, sauté another 2 minutes until fragrant; lower heat and stir constantly to avoid burning.
Add the spices and sauté for a minute more.
Stir in the coconut milk, stock, lentils, and pumpkin puree.
Simmer over medium-low heat for 40 to 50 minutes or until lentils are tender. Be sure to stir occasionally.
Before serving, stir in the red curry paste if you are using it or adjust seasoning with black pepper. For a smoother stew, you can use an immersion blender. Garnish with fresh cilantro or thai basil, serve with crusty bread.