Cover bottom of 9-inch springform pan with parchment. Beat 6 egg whites in medium bowl with mixer on high speed until soft peaks form; set aside. Beat butter and brown sugar in large bowl with mixer until light and fluffy. Add egg yolks, 1 at a time, mixing well after each addition. Blend in melted chocolate, vanilla and salt.
Add 1/3 of the egg whites to chocolate batter; stir gently just until blended. Repeat in 2 batches with remaining egg whites. Pour into prepared pan. Bake 30 min. Meanwhile, prepare Meringue Topping.
Combine chopped chocolate, nuts and cornstarch. Beat 4 egg whites in clean large bowl with mixer on high speed until foamy. Gradually beat in granulated sugar until soft peaks form. Gently stir in chopped chocolate mixture.
Remove cake from oven. Spoon Meringue Topping over cake, spreading to edge of pan to completely cover cake and seal meringue to edge of pan.
Once all the eggs are peeled, slice the eggs in half lengthwise, and carefully scoop out the yolks. Mash yolks with a fork (or push through a mesh sieve for a very fluffy, smooth filling) then stir in lemon juice, mayo, mustard and feta cheese until smooth, creamy filling forms. Spoon filling into egg white halves, or add filling mixture to a piping bag (or large ziploc bag) and pipe into filling for a more festive presentation. Top with roasted red peppers and serve!