Preheat oven to 375°.
In a small bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add eggs, one at a time, beating well after each addition. Beat in ginger and lemon zest.
In another bowl, whisk flour, baking soda and salt; add to creamed mixture alternately with buttermilk, beating well after each addition.
Fill greased or paper-lined muffin cups three-fourths full. In a small bowl, mix topping ingredients; sprinkle over muffins.
Bake 14-16 minutes or until a toothpick inserted in center comes out clean. Cool 5 minutes before removing from pan to a wire rack.
