Combine the flour, salt, sugar and yeast in a large bowl. Add oil and 3/4 cup (185ml) warm water. Use a round-bladed knife to stir until combined. Turn onto a lightly floured surface. Knead for 5 mins or until smooth. Set aside for 15 mins to rest.
Heat a medium frying pan over medium heat. Add the sausage and cook, stirring with a wooden spoon to break into lumps, for 5 mins or until browned.
Grease a slow cooker and line the base and side with 2 layers of baking paper, allowing 2 long sides to extend 5cm up the side. Roll out the dough on a lightly floured surface to a 25cm x 30cm oval shape. Place in the prepared slow cooker, turning the edge to make a 2cm border.
Combine the pizza sauce and diced tomato in a bowl. Spread over the dough. Top with the cheese, sausage, pepperoni, olives, cherry tomato and capsicum.
Cover and cook for 1½ hours on high (or 3 hours on low) or until the pizza base is golden underneath. Use the paper to transfer pizza to a clean work surface. Sprinkle with basil and cut into slices.