Preheat the oven to 375 degrees. Toss parsnips and carrots with rosemary, garlic, 2 tablespoons oil, and salt and pepper to taste. Roast for 25 minutes.
Transfer vegetables to a high-speed blender or a food processor, add water. Puree until thick and smooth; set aside.
In a medium bowl stir together ricotta, oregano, lemon zest and juice, basil and salt and pepper to taste.
In a separate bowl stir together the broccoli, panko, cheese and remaining 2 tablespoons of olive oil.
In an 8-inch square pan, drizzle a thin layer of olive oil. Place a quarter of the sweet potato slices in the bottom, letting them overlap slightly. Add a layer of half the herbed ricotta, another layer of a quarter of the sweet potatoes, the parsnip and carrot puree, another quarter of the sweet potatoes, the remaining herbed ricotta and the remaining sweet potatoes. Add a thick layer of the broccoli crumble.
Cover the pan with aluminum foil and bake for 55 minutes. Remove foil; continue to bake until broccoli is crisp and browned, about 15 minutes more.
You may need to adjust temp and time for altitude and differences in ovens.