Preheat the oven to gas 220°C. Put the passata and olive oil in a pan and bring to a boil. Reduce the heat and simmer for 5 mins, or until thickened.
Empty the pizza base mix into a bowl and stir in 100ml warm water. Mix to a soft dough, then tip out onto a lightly floured surface and knead for 5 mins, or until smooth. Roll out the dough to roughly 24cm in diameter. Transfer to a large, greased baking sheet and turn up the edge of the base for a crust. Leave to stand in a warm place for 10 mins.
Meanwhile, thinly slice 8 olive halves lengthways into 4 to make 32 legs for the spider (each spider has eight). Dice two more olive halves to make eyes for the mozzarella ghosts.
Spread the passata over the base, allowing a 1cm border. Top with the salami and arrange the torn mozzarella in ghost shapes (with room to spread). Position the remaining olives, cut-side down, and arrange 4 spidery legs on either side.
Cook the pizza for 15-18 mins, until bubbling and golden. Remove from the oven and leave to cool for 1 min, before adding the reserved olive eyes to each melted mozzarella ghost. Serve immediately.