Preheat oven to 400 F.
In a large oven-proof skillet, heat olive oil until shimmering over medium heat. Add the onions and cook for 2 minutes. Add the garlic and cook for a minute longer. Add the mushrooms, season all with salt & pepper, and cook for 2 more minutes.
Stir the flour, parsley, thyme, and rosemary into the mushroom mixture until evenly coated for at least a minute to cook the flour.
Add the wine and cooked lentils (I used Trader Joe's). Cook until most of the wine is reduced and absorbed.
Whisk the tomato sauce into the vegetable broth and add with the frozen vegetables and bay leaf, stirring to combine. Simmer for 5 minutes then remove from the heat. Discard the bay leaf.
*** If you're feeding a large crowd, leave the mixture in the skillet.
If you'd rather split the recipe into 2 pie plates, now is the time to do it. Follow the recipe but only bake one of the pies and freeze the other for another day.
Top the filling with the mashed potatoes. You can spoon it on and spread carefully as to not mix in the filling or gravy, or use a piping bag to get fancy. Bake in the pre-heated oven for 15 minutes or until the potatoes are lightly browned.
Remove the pie from the oven and let it rest for 15 minutes before serving.