Distribute berries among 4 individual heatproof dishes. Preheat broiler. Beat egg yolks, superfine sugar, and Grand Marnier in a heatproof bowl with a whisk or handheld mixer on medium. Set bowl over a pan of simmering water, and cook, whisking constantly, 8–10 minutes or until thickened. (Do not let the mixture boil.) Remove bowl from heat, and stir in lemon zest; pour zabaglione over the fruit. Place dishes under broiler for 1 minute or until golden. Serve immediately.