Bring potato and cauliflower to a boil in salted water. Cook until soft.
Blend or mash with roasted garlic, olive oil, nutritional yeast, salt, and pepper until smooth. Set aside.
Heat olive oil in a skillet over medium. Sauté onion and garlic until fragrant. Add carrots and tomato paste; cook until the paste darkens.
Stir in lentils, herbs, salt, pepper, and water. Simmer, covered, until almost tender (20–25 minutes). Add corn or peas and cook until lentils are fully done.
Preheat oven to 350°F (180°C).
Spread lentil filling into a casserole dish or ramekins. Top with mash, smoothing evenly.
Bake for 20–25 minutes, until the topping is golden and filling is hot.
Serve warm, with a simple green salad on the side.
Notes
Sample each component as you prepare, ensuring that every part of the dish tastes delicious on its own.