Rinse the lentils before adding them to a pan with 500ml of boiling water and the stock cube (optional). Boil the lentils for 10 minutes and then leave them simmering for a further 15 minutes. Once the lentils have softened you can drain, rinse and set them to the side.
In a seperate pan cook the spaghetti noodles by adding them to a boiling pan for 10 minutes or until they're completely soft. Once the spaghetti noodles are cooked just drain them and set to the side.
Dice the garlic, and roughly chop the mushrooms and red onion.
Cook the garlic, red onion and mushrooms in a pan until the red onion is starting to soften.
Once the onion is softened add 1 tin of chopped tomatoes, the lentils, spaghetti, dried herbs, salt and pepper.
When the sauce is bubbling you know its ready so get it off the heat and serve.