I happened to make this last night. I literally just threw everything in a pot. I fried onions, mushrooms, sprouts, quorn sausages first, then put in potatoes and lentils, stock, sage, paprika, nutmeg and anything else you like. Was yummy.
fry some onion, diced carrots and celery and a couple of crushed garlic cloves. Add grainy mustard, honey and paprika, plus black pepper. Add a tin of passata and some water, plus dried green lentils. Shove in the oven and ignore for half an hour or so. Then add some sliced veggie hotdog sausages and a diced red pepper and warm through again. Salt and more pepper if needed. I sometimes make double - have it one night with hassleback potatoes and then the next night top it with sliced part cooked potatoes and cheese and shove in the oven until golden.