Preheat the oven to 350°F. Line a 9×5 inch bread pan with parchment paper.
In a bowl, whisk together the melted butter, brown sugar, apple butter, yogurt, eggs, and vanilla. Stir in the shredded zucchini. Add the flour, baking powder, and salt. Mix until combined.
Pour the batter into the prepared pan. If desired, swirl in 2-3 tablespoons apple butter, leaving streaks of apple butter throughout the batter.
To make the cinnamon dollops. Mix the butter, brown sugar, flour, and cinnamon. Arrange the clumps over the batter. Bake for 60-65 minutes or until the center is just set.
To make the cinnamon butter. In a bowl, beat the butter, maple syrup, vanilla, cinnamon, and a pinch of salt. Serve with the warm zucchini bread.
