Heat oven to 350ºF. Place paper baking cups into 12 muffin pan cups; set aside.
Combine flour, sugar, baking powder, baking soda, cinnamon and salt in bowl; mix well.
Combine butter and eggs in bowl; stir into flour mixture just until moistened.
Stir in zucchini.
Fill prepared muffin pan cups three-fourths full with batter.
Bake 22-25 minutes or until toothpick inserted into center comes out clean.
Cool 5 minutes in pan; remove to cooling rack.