01 - Preheat oven to 400°F.
02 - Boil sweet potatoes in salted water for 15-20 minutes until fork-tender. Drain, then mash with olive oil or vegan butter and plant-based milk. Season with salt and pepper. Set aside.
03 - While potatoes cook, heat olive oil in a large skillet over medium heat. Add onion, carrots, and celery; sauté 5-7 minutes until softened. Add garlic and cook 1 minute more.
04 - Stir in lentils, vegetable broth, diced tomatoes, tomato paste, thyme, rosemary, and smoked paprika. Bring to a boil, reduce heat, cover, and simmer 20-25 minutes until lentils are tender and mixture thickens. Add water if needed.
05 - Stir in peas, and season with salt and pepper. Remove from heat.
06 - Transfer lentil filling to a large baking dish. Spoon mashed sweet potatoes over the top, spreading evenly.
07 - Drizzle with a little olive oil if desired. Bake for 20 minutes, or until topping is slightly golden.
08 - Let rest 5 minutes before serving.