Peel the sweet potato: Peel the skin of the sweet potato and cut them into 1 inch cubes. Add the cubed sweet potatoes in the casserole in a single layer with spaces between each other. Collect the condiments like ground allspice, dried parsley, dried thyme, dried rosemary, salt and brown sugar. Drizzle the olive oil and sprinkle the condiments on the sweet potato. Toss to coat the sweet potato cubes with the spices.
Roast the sweet potatoes: Place the casserole with sweet potatoes in the preheated oven on 200°C. Roast the sweet potatoes for 25 to 30 minutes. Flip the sweet potatoes halfway through to ensure even cooking. Rest for 5 minutes, and then serve.