Stir graham cracker crumbs and melted butter together in a bowl until moistened; press crumb mixture evenly into the bottom of a 7-inch round springform pan. Place pan in refrigerator until cold, about 20 minutes.
Beat cream cheese and 6 tablespoons plus 1 teaspoon sugar together in a bowl with an electric mixer until smooth; beat in mascarpone cheese. Stir 3 tablespoons green tea powder into cheese mixture.
Beat cream in a chilled glass or metal bowl with an electric mixer until soft peaks form. Fold whipped cream into cream cheese mixture.
Stir gelatin into warm water in a small bowl until dissolved. Stir gelatin mixture into cream cheese mixture; pour mixture over refrigerated graham cracker crust. Chill in the refrigerator until firm, at least 4 hours.
Dust top of tiramisu with green tea powder and confectioners' sugar; decorate with sliced strawberries.