Peel and chop all the potatoes into rough 2cm chunks. Place the Maris Pipers into a large pan of cold salted water over a medium heat. Bring to the boil, then simmer for 10 to 15 minutes, or until tender, adding the sweet potatoes after 5 minutes.
Drain and leave to steam dry, then return to the pan with the margarine and a pinch of sea salt and black pepper. Mash until smooth, then set aside.
Peel and finely slice the onion, carrots and 2 garlic cloves, then trim and finely slice the celery.
Bash the coriander seeds in a pestle and mortar until fine, then add it all to a medium pan over a medium heat with a good splash of oil. Pick in the thyme leaves, then cook for around 10 minutes, or until softened.
Meanwhile, roughly chop the mushrooms and sun-dried tomatoes, then add to the pan along with the vinegar and 2 tablespoons of the sun-dried tomato oil from the jar.
Cook for a further 10 minutes, then add a splash of wine, turn up the heat, and allow it to bubble away. Stir in the stock, lentils and chickpeas (juice and all), then leave it to tick away for 5 to 10 minutes, or until slightly thickened and reduced.
Pick and roughly chop the parsley leaves, then stir into the pan. Season to taste, then transfer to a baking dish (roughly 25cm x 30cm).
Spread the mash over the top, scuffing it up with the back of a spoon.
Finely slice the remaining garlic clove, then place into a bowl with the rosemary leaves, lemon zest, breadcrumbs and 1 tablespoon of oil. Mix well, sprinkle over the mash, then place in the hot oven for around 10 minutes, or until piping hot through.
Place under the grill for a further 2 to 3 minutes, or until golden, then serve with seasonal greens.