Lightly spray 5.5 litre (22-cup) capacity slow cooker with olive oil.
To make filling, combine all ingredients in a large bowl. Season with pepper.
To make topping, whisk ricotta, egg and half the cheese in a medium bowl until well combined. Season with pepper.
To assemble, spread one-third of the filling over base of slow cooker. Arrange one-third of the lasagne sheets on top, breaking into pieces to cover filling evenly. Top with half the zucchini slices. Repeat layers with another one-third of the filling, one-third of the lasagne sheets and remaining zucchini. Top with the remaining filling, then cover with remaining lasagne sheets.
Spread evenly with topping. Sprinkle with remaining pizza cheese and paprika.
Cover with lid. Cook on LOW for 4 hours and 15 minutes, or until lasagne is tender when tested with the tip of a sharp knife. Turn power off. Stand, covered, for 30 minutes before serving. Serve with cherry tomatoes and basil leaves or a leafy salad.