Preheat oven to 350 degrees. Line your muffin tins and set aside.
Combine flour, cocoa powder, baking soda, and salt in a bowl and whisk to combine. Set aside.
In large mixing bowl, beat sugar, oil, eggs, and vanilla until well blended. Add yogurt and beat to combine.
Add dry ingredients and mix just until combined. Mix in zucchini and chocolate chips coated in 2 tablespoons flour. Divide batter between pans.
For Streusel - Combine all the ingredients in a food processor and pulse until crumbly. Alternately, you can mash the ingredients together in a bowl using a fork, or just smoosh everything together with your fingers. Sprinkle over muffins immediately before baking.
Bake for 50-60 minutes or until a toothpick comes out clean.
Cool 10 minutes in pan on a wire rack; remove from pan, and cool completely on a wire rack before cutting.
(Bake mini loaves for 30 - 35 minutes or muffins for 18 minutes.)
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