For ease in chopping candy slices, dip scissors or knife in flour.
Stir together soda and 1 1/2 tablespoons water until dissolved.
Beat shortening at medium speed with an electric mixer until creamy. Gradually add sugars, beating until fluffy. Add soda mixture, eggs, and next 3 ingredients; beat until blended.
Combine flour, oats, and baking powder. Gradually add to shortening mixture, beating until blended. Drop by rounded tablespoonfuls onto lightly greased baking sheets.
Bake cookies at 350° for 10 to 12 minutes. Remove to wire racks to cool.
Stir together powdered sugar and orange juice; drizzle over cookies.