Preheat oven to 350 degrees.
Prepare the cauliflower and celery root puree. Reserve.
In a large, deep, frying pan or pot, heat oil over medium-high heat. Add onion and carrot. Cook, stirring occasionally, for 5 minutes or until onions start to soften and become glossy.
Add mushrooms and continue cooking and stirring for another 5 mins. Add garlic, cumin and ½ teaspoon salt. Continue stirring and cooking for 2 minutes.
Add tomato paste and sprinkle with the flour. Stir until combined. Pour in the wine and scrape up any brown bits that have formed on the bottom. Add the rinsed lentils and stir. Add the peas and mix.
Add the stock/broth and Worcestershire sauce. Bring to a boil. Reduce heat to a simmer and cook for 25 minutes or until lentils are softened.
Transfer lentil mixture to a baking dish. Scoop the cauliflower and celery root puree on top and spread evenly. Top with Parmesan cheese if using. Place on a tray in case it bubbles over and bake in preheated oven for 20 minutes. If you want to brown the top, turn on the broiler and keep an eye on it until it’s browned to your liking.