Preheat the oven to 200°C (180°C fan) and line a large baking tray with baking parchment.
Break the cauliflower into florets, then whizz in a food processor until it resembles grains of rice.
Transfer the riced cauliflower to a microwave-safe bowl and microwave on full power for 5-7 minutes until tender. Leave to cool slightly.
Wrap the cooled cauliflower in a clean tea towel or piece of cheesecloth, gather the edges and squeeze out as much liquid as possible.
In a large bowl, combine the drained cauliflower with the egg, 120g shredded mozzarella, 30g ground almonds, 1 tsp dried oregano, 1/2 tsp garlic powder, 1/4 tsp salt and a pinch of black pepper. Mix until a dough forms.
Tip the mixture onto the prepared tray and press into a 25-30cm round about 5mm thick, making the edges slightly thicker to form a crust.
Bake on the middle shelf for 20-25 minutes, or until the crust is firm and golden.
Remove the crust from the oven and spread 120ml tomato pasta sauce evenly over the base, leaving a small border around the edge.
Scatter over 125g shredded mozzarella, pepperoni slices (if using) and thinly sliced bell pepper. If you like, top with 2 tbsp grated Parmesan.
Return to the oven and bake for a further 10-15 minutes until the cheese is melted and bubbling and the crust edges are golden.
Leave to cool on the tray for 5-10 minutes before slicing and serving.