- Preheat the oven to 180 degrees C 
- Place the potatoes in a large saucepan and cover with plenty of boiling water 
- Bring to the boil and simmer until soft 
- Meanwhile, heat the oil in a large saucepan 
- Add the onion and cook for a few minutes 
- Add the carrots, celery and garlic and stir 
- Continue cooking on a gentle heat for a few minutes 
- Add the tomatoes, tomato puree and stock 
- Add the lentils 
- Add the mixed herbs, cumin, paprika and chilli 
- Bring to the boil and turn down to a gentle simmer for about 20 minutes 
- Add the frozen peas and green vegetable and stir 
- Cook for a few more minutes 
- When the potatoes are cooked pour on the milk and add the butter 
- Mash with a masher until smooth 
- Place the lentil mixture in the bottom of a casserole 
- Place the mashed potato on top 
- Sprinkle with the cheddar cheese 
- Bake in oven at 180 degrees C for about 40 minutes