Mash bananas with a fork; stir in lemon juice until blended.
Beat cream cheese and sugar at medium speed with an electric mixer until light and fluffy. Add mascarpone, beating until smooth. Add eggs, 1 at a time, beating well after each addition. Stir in banana and vanilla. Pour into Peanut-Graham Crust.
Bake at 325° for 1 hour (center will be slightly soft). Remove from oven; run a knife around edge to loosen sides. Cool on a wire rack; cover and chill 8 hours.
Microwave chocolate and butter in a 1-quart microwave-safe bowl at HIGH 60 seconds; stir until smooth. Let stand 30 minutes.
Remove sides of springform pan. Spread three-fourths of melted chocolate around sides of cheesecake. Arrange Caramelized Bananas on top; drizzle with remaining chocolate.
*1 (8-ounce) package cream cheese, 2 1/2 tablespoons sour cream, and 2 tablespoons whipping cream may be substituted for mascarpone cheese. Beat ingredients well at medium speed with an electric mixer. Use 1 cup mixture for cheesecake recipe, reserving remainder for other uses.