Heat your oven to 180°C/Fan 160°C/Gas 4. Halve the marrow length ways. Scoop out the seeds. Pop the marrow halves on a baking tray. Roast in the oven for about 25 mins till they’re tender when you press them with a fork.
While the marrow halves roast, peel and finely chop the onion. Halve the pepper. Scoop out the seeds and white bits. Finely chop the pepper.
Warm 1 tsp oil in a pan. Add the onion and pepper. Season. Fry over a low heat for 5 mins till the veg are soft and glossy. Stir often.
While the veg cook, peel and crush the garlic. Finely slice the chard stalks and slice the leaves. Dice the tomatoes. Stir the garlic into the pan. Cook and stir for 1 min till the pan smells sweet and aromatic.
Stir in the chard stalks and tomatoes. Gently fry for 5 mins. Stir often to break the tomatoes up a little. Drain and rinse the lentils. Tip them into the veg. Add the chard leaves and 2 tbsp water. Fry for 5 mins to warm everything through. Stir now and then. Taste and adjust the seasoning.
Take the marrow halves out of the oven. Drain off any water. Spoon enough lentils into the middle of each boat to just fill them. You may have some left over. Cover the pan and set aside.
Grate 20g of the Parmesan and measure out 1 ½ tbsp. Sprinkle it over the marrow boats. Return to the oven and roast for 15-20 mins till golden. Serve straight away with any extra lentils on the side and the basil scattered over the top.