Preheat oven to 450°F degrees
Line a baking sheet with parchment paper, grease then set aside
In a food processor, rice cauliflower florets
Transfer cauliflower rice (3 cups) to a microwave-safe dish and microwave on high for 8 minutes, until cooked or steam on stovetop
Place cauliflower rice in a tea towel and twist it to squeeze as much moisture as possible
Transfer cauliflower rice to a mixing bowl, add egg, 1/2 c mozzarella, oregano, salt and pepper and mix well
Spread cauliflower mixture onto lined baking sheet and form into a large rectangle
Bake for 10 minutes
Remove from oven
Spread tomato sauce over most of the dough, leaving a 2-inch border on one side
Spread 1/4 cup mozzarella, then the meat/toppings, then the remaining cheese
With large spatula lift the longer sides of the crust and roll into stromboli shape
Flip seam down and tuck/fold the shorter side to close the stromboli
Cut slats in the top
Sprinkle with grated Parmesan and oregano, if desired
Bake for an additional 12 minutes
Cool a few minutes before slicing and serving