Preheat the oven to 150°C/300°F. Line a baking sheet with parchment paper and draw on a 23cm circle.
Make the meringue in a large clean bowl. Whisk the egg whites and salt into stiff peaks. Slowly add the sugar, a third at a time, whisking well between each addition until the mixture is stiffened and shiny.
Sprinkle in the cornflour, vinegar and vanilla extract, then fold in gently with a metal spoon.
Pile the meringue onto the paper circle and make a deep hallow in the centre.
Put in the oven and reduce heat to 120°C/240°F. Cook for 1½ hours until pale brown but a little soft in the centre. Turn off the oven, leave the door ajar and allow to cool completely.
To make the filling, whip the cream in a bowl with vanilla seeds and lemon rind until thickened and just holding its shape.
To serve, gently peel the parchment paper off the Pavlova and carefully transfer to a serving plate or cake stand. Pile on the cream mixture and arrange the strawberries, blueberries and kiwi slices on top. Serve straight to the table and cut into slices to serve on individual plates.