Heat oil in a large, deep frying pan over medium-high heat. Add mince. Cook, breaking up with a wooden spoon, for 5 minutes or until browned. Add onion, carrot and harissa. Cook, stirring, for 5 minutes or until onion is softened. Add tomato and stock. Bring to a simmer. Reduce heat to medium-low. Simmer for 7 minutes or until thickened slightly. Stir in beans. Cook for 4 minutes or until beans are just tender.
Step 2 Meanwhile, place sweet potato in a microwave-safe bowl. Add 1/4 cup cold water. Cover. Microwave on HIGH (100%) for 6 minutes or until tender. Drain. Mash until smooth. Add cinnamon and butter. Stir with a wooden spoon until combined. Season with salt and pepper.
Step 3 Preheat grill on high. Spoon mince mixture into a 2-litre-capacity flameproof baking dish. Dollop with mash. Grill for 2 minutes or until mash is lightly browned. Serve.