In a small measuring cup, mix the lemon juice with the sugar and 1/4 cup water until the sugar is dissolved. Set aside.
Place the cream cheese, lemon curd and heavy cream in a food processor and process until smooth and a bit fluffy.
To assemble the tiramisu, place half the ladyfingers in the bottom of an 8-inch square baking dish, breaking a few to fit, and drizzle with half of the lemon syrup. Top with half the lemon cream and 1 cup mixed berries. Repeat the layers, using the remaining ladyfingers, syrup and lemon cream.
Cover with plastic wrap and chill at least 8 hours or overnight. Before serving, top with the remaining 2 cups of berries and dust with powdered sugar. Serve with whipped cream on the side.