In a deep pot, add the sweet potatoes and enough water to cover. Bring to a boil, salt the water and cook the potatoes until tender, about 15 minutes. Drain.
While the potatoes are working, in a bowl, season the turkey with salt and pepper. Add the breadcrumbs, scallions, parsley and thyme. In a small bowl, beat the egg with the milk; mix into the turkey mixture. Shape the meat into 4 oval patties about 1 inch thick. In a large skillet, heat the EVOO, 1 turn of the pan, over medium-high heat. Add the patties and cook, turning once, until browned, about 15 minutes.
In a medium saucepan, melt the butter over medium heat. Add the onion and cook until softened, about 6 minutes. Add the orange peel and season with salt and pepper. Sprinkle the flour on the red onion and cook for 1 minute, then whisk in 3/4 cup chicken broth and the orange juice; cook until thickened, 30 seconds. Whisk in 2 tablespoons brown sugar, the ketchup, mustard, Worcestershire sauce and hot sauce. Lower the heat and simmer for 5 minutes.
Mash the potatoes with 1 to 1 1/4 cups chicken broth. Stir in the remaining 2 tablespoons brown sugar; season with salt and pepper. Serve with the turkey patties and the gravy on top.