Bring a large pot of water to a boil. Add the sweet potatoes. Boil until fork-tender, about 15-20 minutes. Drain very well. Mash with the maple syrup, salt, and cayenne. Set aside.

Heat 1 tablespoon canola oil in a medium skillet over medium heat. Add the turkey in one piece, as it comes from the package. This allows for good caramelization and flavor. Once caramelized and brown, flip the turkey to sear the second side. Use a wooden spoon to break up the chunk and cook until just no longer pink in the center, about 3 minutes — not longer, since turkey dries out easily. Transfer to a bowl, chopping more with the spoon. Set aside.

Add remaining 2 teaspoons canola oil to the pan. Heat. Add the onion and garlic. Use a wooden spoon to stir up the fond from the drippings. Cook until the onion caramelizes, about 6-7 minutes. Add the oregano, sage, and black pepper. Cook for 3 minutes longer, until the spices are fragrant. Add the turkey to the pan. Add the stock and dissolved cornstarch. Stir well to distribute the onions. Bring to a simmer. Cook until slightly thickened. Add the peas and cook until they are shiny, 3 minutes. Transfer to a 9 x 13-inch oven-to-table casserole dish. Spread the sweet potato in an even layer over the turkey.

Preheat oven to broil. Sprinkle the top of the sweet potatoes with the brown sugar. Place the dish 3-4 inches from the heating element and broil for 5-6 minutes until the brown sugar starts to caramelize. Serve hot.