Preheat the oven to 200°C. In a large bowl, combine the bread mix with the rosemary, then make up the dough and knead following the packet instructions. Allow the dough to rest for about 5 minutes.
Using a rolling pin, roll out the dough to approximately fit a shallow roasting tin that measures about 27 × 40 cm. Push the dough into the corners to make a neat fit. Cover lightly with a clean tea towel and set aside in a warm place while you prepare the topping.
Place the anchovies in a small bowl and cover with the milk. Allow to soak for 5 minutes, then drain and finely chop. (This soaking will remove the excess salt from the anchovies.)
Spread the tomato purée all over the pizza base, right up to the edges. Scatter the sliced mushrooms over the pizza, then flake over the tuna. Dot the tomato pieces, capers and chopped anchovies all over. Using a teaspoon, add little mounds of ricotta over the top, then drizzle evenly with the olive oil.
Bake for 25 minutes or until well risen with a golden crust around the edge. Transfer to a wire rack to cool slightly, then cut into six pieces. Scatter the basil over the slices and serve warm.
*If your children do not like the strong flavours of anchovies and capers, replace them with diced red capsicums, corn or cubed smoked ham. *You could add a handful of sunflower seeds, pepitas or sesame seeds to the dough for a nutty flavour and texture.