12 graham crackers (2 1/2-inch squares), made into crumbs
4 tsp. butter
4 bananas, thinly sliced on the diagonal
2 tbsp. fresh lime juice
1 envelope unflavored gelatin
1/3 c. sugar
1 1/2 c. plain fat-free yogurt
1 tsp. vanilla extract
grated lime zest

Preheat oven to 350°F. Spray 9-inch pie plate with nonstick cooking spray.

In bowl, combine crumbs and butter with fork. Press onto bottom and up sides of pie plate.

Bake until firm, 3 to 5 minutes; cool.

In another bowl, toss bananas with lime juice; reserve 1 cup. Arrange remaining bananas over crust.

In saucepan, sprinkle gelatin over 1/2 cup cold water; let stand 2 minutes. Add sugar; cook over medium-high heat, stirring constantly, until mixture boils and gelatin and sugar dissolve, 2 to 3 minutes. Remove from heat. Whisk in yogurt and vanilla. Pour into pie plate. Arrange reserved bananas over pie; sprinkle with lime zest. Cover with plastic wrap. Refrigerate until chilled, 2 to 3 hours.