Preheat oven to 180C/350F
Heat the oil in a large pan, add the onions and cook gently for 5 minutes until softened.
Add the carrots, celeriac and potato and fry gently for a further 5 minutes.
Add the garlic and thyme and fry gently for a minute until aromatic.
Add the lentils, tinned tomatoes and stock.
Fill the tomato can with water to collect all the leftover juice and add to the pan.
Bring to the boil then reduce heat to a simmer and cook for 20 minutes with the lid on.
Remove the lid and cook for a further 10 minutes or until the vegetables are tender, the lentils are cooked and the liquid has nearly all evaporated off.
Pulse nuts together in a food processor until roughly chopped. Transfer to a bowl.
Add breadcrumbs, herbs, paprika, sunflower seeds and salt and pepper to taste to the nuts. Stir to combine.
Transfer the lentil mixture to a large oven proof dish. Top with the nut crumble and bake in the preheated oven for 15 minutes.
Serve and enjoy!