Prepare angel cake as directed on package, except pour 1/3 cup of the thawed orange juice concentrate into a 2-cup measure; add enough water to the concentrate for the mixture to equal the amount of water called for in the package directions.
Continue with package directions, baking the batter in an ungreased 10" tube pan according to package directions.
Immediately invert cake (leave in pan); cool completely.
Loosen sides of cake from pan; remove cake from pan.
For topping, in a medium bowl gently stir together the thawed topping and yogurt. Fold in remaining orange juice concentrate.
Spread topping mixture over top and sides of cake. If desired, garnish with citrus roses made from grapefruit or orange peel. Store in the refrigerator.
Citrus Rose: Cut the peel from stem end of a Florida Orange or Grapefruit, forming a circular base (do not sever). Continue cutting a strip of peel about 3/4" to 1" wide in a spiral motion to opposite end of fruit, making one lon g, continuous strip and slicing thinly (do not cut into white membrane). Start coiling strip tightly, beginning at end opposite base. Coil the strip onto the base to form a rose. Garnish with mint leaves and small strips of peel, if desired.