Preheat the oven to 400F. Unroll the pie crust and press into a 9-inch pie dish, smoothing the bottoms and sides. Prick all over with a fork and crimp edges. Line with parchment (with an overhang) and fill with pie weights, dry beans, or rice to prevent puffing. Bake 10 mins, then lift out parchment with weights and bake uncovered until edges are golden, 5 to 8 mins more. Remove from the oven, reduce temp to 375F, and cool the crust while you prepare the filling.
In a large pan over medium-high heat, melt the butter then add the onions. Cook, stirring often, until the onions are starting to become tender and translucent (3-5 mins), then add the zucchini, garlic, salt, pepper, and oregano. Cook, stirring often, for 6-8 mins until the zucchini is tender but not completely falling apart, then remove from the heat.
In a large bowl, beat the eggs and add the Tillamook mozzarella, cottage cheese, basil, and parsley. Add the zucchini + onions and stir to combine.
Brush the dijon mustard along the inside of the pie shell (this will add a nice tangy flavor!). Pour in the filling and spread into one layer. Option to arrange the zucchini rounds nicely on top.
Bake for 35-40 mins until a knife comes out clean from the center. Let cool for 5 mins, then sprinkle with parsley, slice and enjoy!
