Preheat oven to 200°C/180°C fan/gas 6 and lightly oil the bottom of a large oven proof dish. In a mixing bowl, combine the tuna, ricotta cheese, mayonnaise, olives and spinach.
Fill the dry cannelloni tubes with the tuna mixture using a teaspoon, or a piping bag minus the nozzle (you can also use a thick freezer bag with the corner snipped off). Make sure you pack the mixture tightly into the pasta tubes and place them in the oven proof dish in a single layer.
Mix the passata and red pesto in a large measuring jug and pour over the filled cannelloni. Sprinkle with cheese and cover with aluminium foil.
Bake for 20 minutes and then remove the foil and bake for a further 20 minutes, or until the top is golden and bubbling. Check the pasta is cooked with a skewer before serving with a crisp green salad and crusty bread.