Heat a large frying pan and crumble in the mince. Fry over a high heat for 8 mins until completely browned. Pour in the tomato sauce and leave to bubble, uncovered, for 15 mins until thickened. Taste and season if you need to.
Heat the grill. Cut the baguette in half lengthways, then cut the halves into 2 pieces. Place the bread, cut-side up, on a baking tray and grill for 2-3 mins until lightly toasted. Remove from the grill and divide the mince between the pieces. Scatter over the torn pieces of mozzarella.
Grill for 3-4 mins more, until the cheese is bubbling and golden. Scatter with the basil and serve with a salad, if you like.