Preheat the oven to 375 degrees F (190 degrees C).
Cut off the end of the Butternut Squash (1/2).
Peel the butternut squash, scoop out the seeds and cut into large chunks.
Peel and cut the Russet Potato (2) into cubes.
Put the cubed potatoes and butternut squash in a pot and submerge with water.
Season water with a large pinch of salt and cook until tender.
In a heated pan, add Olive Oil (1 tablespoon), Onion (1) and Garlic (3 clove). Cook gently until translucent.
Add Carrot (3) and Celery (2 stalk). Season with Salt and Pepper (to taste). Saute for 10 minutes, but do not brown.
Add Mushroom (2 cup), Fresh Thyme (1 tablespoon) and salt and pepper. And allow to cook down. Then add Tomato Paste (1 teaspoon) and Worcestershire Sauce (1 tablespoon). Turn off the heat and set vegetable mixture aside.
In a large bowl, combine French Green Lentils (1/2 cup), Breadcrumbs (1/2 cup), Egg (2), Fresh Parsley (1 handful), mix well. Season with salt and pepper.
Add in mushrooms mixture.
When the potatoes and squash are done, drain, season with salt and pepper. Add Butter (2 tablespoon) and olive oil. Mash until the mixture are smooth.
In a casserole pan, even out the filling. Pile topping in the middle and spread evenly. Put in the oven for 25 minutes. The pie should be golden on top.