Heat the olive oil in a large frying pan over a medium heat and gently fry the chopped onion, garlic, carrots and celery for 5-10 minutes until softened.
Add the remaining ingredients except for the lentils and chives season to taste with salt and freshly ground black pepper. Bring to a simmer for 10 minutes until the vegetables are tender and the sauce has reduced. Stir the lentils and chives into the sauce.
Mash the potatoes for the topping.
Spoon the lentil mixture into a medium pie dish and top with the potatoes.
Place the dish onto a baking sheet and bake the pie for 25-30 minutes, or until the potato is golden brown.