For Ganache: Bring heavy cream to boil in saucepan on medium heat. Remove from heat; add chocolate and peanut butter. Let stand 5 min. Starting from center, slowly stir in a circle until mixture is smooth and shiny. Cool to room temperature. Fold in cookie pieces. Refrigerate at least 3 hours or overnight. When ready to use, whip until soft peaks form.
For Cake: Stir 6 oz. cookie pieces into cake batter. Divide batter evenly among 3 parchment paper-lined 9-inch cake pans. Bake as directed on cake package. Cool completely in pans on wire rack. Remove cakes from pans. Level cakes to 1/2 to 5/8-inch high.
Line bottom of 4-inch high x 9-inch cake pan with parchment paper. Add 1 cake layer. Spread whipped Ganache over top of cake. Top with 2 oz. of the remaining cookie pieces, pressing into Ganache. Top with second cake layer, pressing so it adheres to Ganache. Refrigerate until firm.
For Strawberry Cream: Soak gelatin sheets in large bowl of cold water. Combine sugar and strawberry powder; set aside. Whip cream to soft peaks; refrigerate until ready to use. Squeeze water out of gelatin sheets. Warm gelatin in a bowl over a hot water bath until melted. Combine sugar mixture, strawberry puree and melted gelatin in saucepan. Heat on low heat, stirring constantly until sugar is dissolved. Remove from heat and stir in lemon juice. Cool to 95°F. (The next step should not be done unless cake assembly has begun and you are ready for the Strawberry Cream layer.)
Gently whisk one-third of the whipped cream into the strawberry mixture. Repeat with remaining whipped cream, adding one-third at a time. Immediately pour onto cake layer in pan, spreading evenly. Sprinkle with remaining 2 oz. cookie pieces. Add third cake layer, pressing firmly into Strawberry Cream. Refrigerate until fillings are firm. Carefully remove cake from pan onto large plate. Refrigerate until ready to frost with Meringue.
For Meringue: Place egg whites in bowl of mixer fitted with wire whisk attachment. Make an Italian Meringue by bringing sugar and water to a rolling boil, brushing down side of pan as necessary. When sugar mixture reaches 235°F, start whipping egg whites. When whites are foamy, gradually add hot sugar mixture, whipping on high speed. Continue whipping until mixture is cool. Sprinkle peanut powder over meringue, then fold in until completely combined. Immediately remove cake from refrigerator and frost top and sides using all of the Meringue. Sprinkle cookie pieces over top of cake. Cut into 8 slices.