Squeeze the excess water from the spinach and put in a bowl. Add the ricotta, garlic, cream, nutmeg and salt and pepper, and stir together until evenly combined.
Cook the cannelloni tubes in a large saucepan of boiling water for 5 minutes, or until just al dente. Drain well and immediately refresh under cold water. Pat dry with kitchen paper.
Lightly oil 4 individual gratin dishes with spray oil. Cut down one side of each cannelloni tube and open out flat. Spoon 2 tablespoons of the spinach and ricotta mixture down one side and roll the pasta up to form tubes once more. Divide between the prepared dishes.
Combine all the salsa ingredients in a bowl, then spoon over the cannelloni. Scatter with the Parmesan. Cover the dishes with foil and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 20 minutes. Remove the foil and bake for a further 10 minutes until bubbling and golden. Serve immediately.