Bake lemon chiffon cake mix as directed on package. Split to make 3 layers. Place on aluminum foil-covered baking sheet. Prepare Lemon Filling; reserve about 1/4 cup. fill layers with remaining filling.
Heat oven to 400F. Beat 4 egg whites until foamy. Beat in 1 cup brown sugar (packed), 1 tbsp. at a time; continue beating until stiff and glossy. Do not underbeat. Fold in 1 tsp. grated lemon peel and 1 tbsp. lemon juice.
Frost side and top of cake with meringue. Bake 8 to 10 minutes or until light brown. thin reserved filling with small amount of hot water; spoon over top of cake, allowing some to drizzle down side.