Preheat the oven to 180°C
Start with the red lentils. Place in a saucepan with water and bring to the boil. Simmer for 15-20 minutes until cooked, then drain and set to one side. We will add the lentils to the filling later on.
Take the sweet potatoes and prick each one well with a fork (at least 12 times). Coat the skins in olive oil with a pinch of salt. Place them in the microwave for 5-7 minutes until just cooked through. If you prefer to oven bake them you can do so by preparing them in the same way and baking them for 45-60 minutes at 180 degrees Celsius.
When ready, remove the sweet potatoes from the microwave and let them cool for 5-10 minutes.
While they are cooling, add the butter to a frying pan and sautee the spring onions and spinach for a few minutes until soft. Set aside.
Returning to the sweet potatoes, slice them in half and scoop out the sweet potato centre. Remember not to scoop right down to the skin. Leave a thin layer of sweet potato on the skin, just enough so that it can stand upright.
Take the empty sweet potato skins and line them up in an oven dish. Drizzle with oil. Bake in the oven for 5 minutes to make them nice and crispy.
In the meantime add the sweet potato to a bowl with the cream cheese, sour cream, sauteed spinach and spring onions, and cooked lentils. Season with salt and pepper if desired. Mash together with a fork until well combined.
Remove the sweet potato skins from the oven.
Fill each sweet potato skin with the mixture and sprinkle with grated cheddar cheese.
Place in the oven for 10-15 minutes or until the cheese is melted and golden.