Heat the olive oil in a large saucepan over medium heat. Add the diced onion and cook for 5 minutes until soft.
Add the minced garlic and cook for 1 minute until fragrant.
Add the red lentils, chopped tomatoes, tomato puree, oregano and basil. Stir well.
Pour in 400ml of water and bring to the boil. Reduce heat and simmer for 20 minutes, stirring occasionally, until the lentils are soft and the sauce is thick.
Meanwhile, cook the pasta according to the packet instructions. Drain and serve with the lentil bolognese on top.