Step 1Heat oil in a large frying pan over medium heat. Add onion and garlic. Stir for 2-3 minutes or until soft. Stir in the passata, water and basil. Bring to boil. Season. Remove from heat.
Step 2Combine the spinach, ricotta and egg in a bowl. Season. Place in a sealable plastic bag. Cut 1 corner off the bag to make a hole. Pipe the spinach mixture into the cannelloni tubes. Transfer to a plate.
Step 3Place 1 cup of the tomato mixture in the slow cooker. Top with filled cannelloni tubes, in a single layer, and the remaining tomato mixture. Cook, covered, on high for 4 hours or until cooked through and tender. Divide among plates. Top with shaved parmesan (or vegetarian hard cheese) and rocket leaves