This is a very easy dish to make and really good. As you can see here I used tomatoes, zucchini, and parsnips. The vegetables have been sliced lengthwise but you do them as you like them. You can use any vegetable for this dish. Off camera there is a little collard greens and some onions that had been previously sweated off. I used them too so there was quite a selection. Be sure to par cook any root vegetable you may want to use except for the potatoes. If not they will not be cooked at the same time as the squash.
Layer the vegetables as you would like them. Put a little garlic and a little thyme between the layers and don't forget to season as you go. Once you get to the potato part it will be too late. Slice the potatoes and arrange them tastefully on top of the dish. Pour a little of the vegetable stock over the whole thing and brush the potatoes with virgin olive oil. Cook in a medium oven.
As for the gravy! I chopped up a little garlic and onion and sweated them off in olive oil. I put in a little extra olive oil. Then I added a little bit of flour and cooked that for a minute or two. This gave me a roux. I slowly added some vegetable stock to that and brought it to the correct consistency. I added some bay leaf and a few whole cloves of garlic. I left that to cook slowly on the side of the stove while the pie was cooking. When the pie was cooked I added a little more chopped garlic to the gravy to refresh. Then I added a little sour cream and strained it. I then added a little chopped parsley and it was finished