For the berries: Mix together the berries, lemon juice, limoncello and sugar in a medium bowl. Crush the berries gently, using the back of a fork. Set aside for at least 30 minutes to let the juices develop and the flavors mingle.
For the limoncello zabaglione: Fill a medium saucepan with 2 inches of water and bring to a simmer over medium heat. In a heat-proof medium bowl that fits comfortably over the saucepan without touching the water, combine the egg yolks, limoncello, sugar, lemon zest and lemon juice. Using an electric mixer, beat on low speed until smooth and incorporated. Place the bowl over the simmering water and continue beating until a thick ribbon remains in the mixture when the beaters are lifted out, about 10 minutes. Remove the bowl from the saucepan and continue to beat for another 2 minutes to prevent the egg from cooking. Cool to room temperature.
To serve, place a 3/4-inch-thick slice of pound cake on a plate. Top with a spoonful of the berries and a dollop of the zabaglione.