Preheat your oven to 350F. Lightly grease a 9x13 pan.
Put the butter and chocolate in a saucepan or microwave safe mixing bowl. If using the microwave, do an initial 1 minute burst, then stir thoroughly. Put it back in for 15 seconds, and stir again. The chocolate should completely melt as you stir. If not, do another 15 second burst. If you use the stove, keep the heat very low and stir constantly, just until the chocolate has melted.
Stir in the sugar and vanilla. Beat in the eggs, one at a time.
Blend in the flour, then fold in the zucchini, walnuts, and chocolate chips.
Turn the batter into your pan and spread out evenly.
Bake for about 30 minutes, checking on the early side. The brownies will look dry on top, and the center should be set. Don't over bake.
Let the pan cool on a rack for at least 15 minutes before devouring. Note: if you want neat squares, let your brownies cool completely before slicing.
Recipe originally published in 2012, updated in 2021