In a large bowl, mix the strawberries, raspberries, blueberries, 2 tablespoons sugar and mint; set aside
In a small bowl, beat cream until it begins to thicken. Beat in remaining sugar. Add lemon juice and zest; beat until soft peaks form. Cover and refrigerate until serving.
Spread butter over both sides of cake slices. Grill over medium heat for 1-2 minutes on each side.
Serve with berry mixture and whipped cream on a serving platter.
Notes
This dessert is packed with antioxidants from all the berries used, and also it is packed with vitamins.