Rise the lentils then put them into a large saucepan, cover with water, bring to the boil and then turn the heat down to a simmer.
Add the marmite and olive oil and stir through. Leave to simmer for around 20 minutes (or until the water has been absorbed). You need to be sure the lentils are cooked through, they should be hard but soft (add more water to continue cooking if they're not turning in to a soft paste).
While the lentils are cooking preheat the oven to 180˚C (350˚F) and grease and line a loaf tin.
Once the lentils have turned into a soft mix add the chopped onion, 'cheese', rosemary, garlic, salt, flour and nutritional yeast. Stir through thoroughly to make sure all the ingredients are well mixed.
Fill the loaf tin with the mixture. Bang the tin on a surface a couple of times to make sure the mixture has properly filled the load tin and has a level top.
Cook in the over for 30 minutes.