Frozen Greek Yogurt Blackout Pie

Break up graham crackers and transfer to a food processor. Add oats, cocoa powder, brown sugar, and salt. (Alternatively, you can finely crush graham crackers in a medium bowl with a smaller bowl into very fine crumbs, then combine with remaining ingredients. The oats can be pulverized with a spice mill or mortar and pestle.) Pulse until finely ground, then add butter and pulse until combined. The crust should hold together when squeezed, but break apart when firmly poked with a finger. Add 1 more Tbsp. melted butter if needed to get crust to come together.

Press crust into bottom and two-thirds of the way up the sides of pie dish in an even layer. Freeze 10 minutes before filling.

Do Ahead: Crust can be made 1 week ahead. Cover with foil and keep frozen.

Melt chocolate and ½ cup oil in a small saucepan over low heat. Let cool slightly. Transfer to a large bowl, then add 1½ cups yogurt and ½ tsp. salt and stir to combine.

Using an electric mixer on medium-high speed, beat egg whites in a medium bowl until white and foamy, about 1 minute. With the mixer running, gradually add ½ cup brown sugar, then continue to beat until stiff peaks form, about 3 minutes longer. Add one-third of meringue to chocolate mixture and fold in thoroughly but gently with a large rubber spatula (this will help lighten it so that the rest of the meringue will be easier to add without deflating it). Add remaining meringue and fold in until no streaks remain. Transfer to prepared crust, keeping filling inside edge of crust and mounding into center if needed. Freeze pie until firm, at least 3 hours. (To freeze overnight, let it sit at room temperature 30 minutes to temper before serving, which will make it easier to slice.)

Combine remaining ¾ cup yogurt, 1 Tbsp. sugar, and a pinch of salt in a small bowl. Dollop yogurt mixture onto pie or onto slices before serving. Drizzle with oil, then sprinkle with cocoa nibs (if using).

Do ahead: Pie can be made 1 week ahead. Cover and freeze. Yogurt topping can be made 1 week ahead. Cover and chill.