Heat 2 TBSP of margarine in a large skillet or cast iron pan* on medium heat
Add 1/4 of mushrooms and cook until browned on both sides, turning once during the process. Repeat with remaining mushrooms, continuing to work in batches to avoid overcrowding the pan. (Mushrooms that are crowded and touching each other in the pan will steam as opposed to brown.)
When all mushrooms are browned, season with salt and pepper and set aside.
Heat 2 TBSP of margarine in a deep dutch oven, or soup pot.
Add onions, carrots, and celery and saute until moisture is released and vegetables are just beginning to brown.
Add salt, pepper, and herbs de provance and cook for another minute.
Clear an area in the pot and add tomato paste and cook for ~2 more minutes until tomato paste is beginning to brown.
Add lentils, dried mushrooms, bay leaf and ~3 cups of broth to pot and bring to a simmer.
Simmer, covered for ~1 hour, stirring frequently and adding more broth as needed.
While lentils are cooking, make potato and parsnip topping and preheat oven to 400 degrees to prepare for baking the dish.
Add potato pieces to a pot of salted, room temperature water and bring to a boil.
In a separate pot of salted water, add the parsnip pieces and bring to a boil.
When potatos and parsnips are softened and can easily be pierced with a knife, drain them and combine them in a single pot.
Add butter, roasted garlic (peel it from the skin), rosemary and thyme and mash to combine.
Add broth or non-dairy milk a little at a time until the desired consistency for mashed potatoes is reached.
Season with salt and pepper and set aside.
When lentils are cooked, add 1/2 cup of red wine to pot and cook for another 2-3 minutes.
Check the consistency of the lentil and mushroom mixture. It should be a very thick stew. If it is too thin, you can cook longer, uncovered to thicken it, or mix 1 TBSP of cornstarch with 1 TBSP water and add to the mixture to thicken.
Remove lentil mushroom mixture from heat and stir in parsley and sherry vinegar.
Transfer lentil and mushroom mixture to a lightly greased casserole dish and gently spoon potato parsnip mixture over the lentil mixture.
Gently smooth out potato mixture so that the entire casserole is covered with the potato mixture.
Cook dish at 450 degrees for 20-30 minutes, until potato topping is beginning to brown.
Remove from oven and let stand for 15 minutes before serving.