Preheat oven to 450° F (225°C). Line baking sheet or pizza pan with parchment paper.
Cut leaves and stem off of cauliflower. Cut into smaller pieces. Place in food processor in batches and pulse into small rice-like pieces. Place in a large microwaveable bowl. Cover and microwave on high for 5 minutes; let cool and pat dry with paper towers. Add parmesan and mozzarella cheeses, eggs, basil and oregano. Press and shape cauliflower mixture onto prepared pan to create an 11 inch (28 cm) round pizza crust about a 1/2 inch (1 cm) thick.
Bake for 25 minutes or until golden brown and set. Let cool slightly.
Spread pizza sauce over top of crust; sprinkle with half of the mozzarella. Scatter pepper, mushrooms (if using), and olives all over. Sprinkle with remaining mozzarella.
Bake for about 10 minutes or until cheese is melted and golden. Sprinkle with arugula.