Preheat your oven to 425°F and line a baking sheet with parchment paper.
Using a food processor, pulse the cauliflower florets in batches until they resemble fine rice grains.
Place the riced cauliflower in a microwave-safe bowl. Cover and microwave on high for 8 minutes until tender.
Let the cauliflower cool slightly, then transfer it to a clean kitchen towel. Wrap up and squeeze firmly to remove as much moisture as possible.
In a medium bowl, combine the mozzarella, Parmesan, and cheddar cheeses. Set aside half of this mixture for topping.
Mix the remaining cheese with the cauliflower, egg, basil, parsley, garlic, salt, and pepper until fully combined.
Shape the cauliflower mixture into an 11x9-inch rectangle on the lined baking sheet.
Bake for 20–25 minutes, or until the edges turn golden brown.
Sprinkle the reserved cheese mixture on top, then bake for an additional 10–12 minutes until melted and bubbly.
Cut into 12 breadsticks and serve warm with marinara sauce, if desired.