Add the prosecco and strawberry jam to a large bowl. Whisk to combine. Set aside.
Place 28 ladyfingers in a large pan so they lie flat. Pour the champagne mix on top. Set aside. They should soak for at least 10 minutes, which is about the time it will take to slice the strawberries and prepare the mascarpone filling.
Add the heavy whipping cream, powdered sugar, and vanilla to a large mixing bowl. Using a hand mixer, mix until soft peaks form, about 3-4 minutes.
Add the mascarpone and mix until stiff peaks form, about 2 minutes. Set aside.
Place the strawberries into a bowl with the lemon juice and toss to combine.
To assemble, spread ⅓ of the whipped cream mascarpone mixture into the bottom of a 9×9-inch pan or baking dish.
Lay 12-14 ladyfinger cookies in a single, even layer so they lie flat without overlapping.
Spread another â…“ of the cream mixture over the ladyfingers.
Place half of the fresh fruit on top of the cream, so they lie flat. Continue with the next and final layers.
Cover with plastic wrap and refrigerate for at least 5 hours of chilling time or overnight.