Preheat oven to 200°C (180°C Fan) or 400°F
Peel and dice the onion, placing it into a large casserole dish along with the tinned lentils (unstrained) and wholewheat fusilli.
Place all other ingredients in a medium saucepan, mix bringing to a boil.
Once the sauce reaches a boil, pour it over the ingredients in the casserole dish evenly distributing the sauce with the ingredients.
Cover with aluminium foil and bake for 60 minutes. Remove from oven and leave to cool for at least 10 minutes before serving.