This frosting is easy to make and not to sweet.

2 tbsp flour
1-2 cup "milk" soy, almond rice... your choice
1/2 cup sugar
1/2 cup margarine
1 tsp vanilla extract (I've used almond extract also)

Cook flour and milk together over medium heat, stirring constantly until
it thickens. Remove and cool.

In a separate bowl, beat sugar, butter and vanilla together for 4
minutes. Add cooled flour and milk mixture. Beat an additional 4
minutes. Spread on cooled cake.