Heat oven to 350F. Spray cookie sheets with cooking spray. In medium bowl, mix cookie ingredients until well blended.
Drop dough by rounded tablespoonfuls about 2 inches apart on cookie sheets.
Bake 9 to 11 minutes or until set. Cool 2 minutes; remove from cookie sheets to cooling rack. Cool completely, about 30 minutes.
In 2-quart saucepan, melt chocolate and butter over low heat, stirring occasionally.
Remove from heat. Stir in powdered sugar and 3 tablespoons of the hot water until smooth. (If frosting is too thick, add additional water, 1 teaspoon at a time.)
