Preheat your oven to 200°C (400°F). While it heats, toss the grated potatoes with salt and pepper to season them evenly. Spray an 8-inch pie dish or quiche pan with oil, then press the seasoned potatoes firmly into the bottom and up the sides to create an even crust—I like to use the bottom of a measuring cup to pack them down really tight so they hold together. Spray the top of the potato crust lightly with oil to help it brown and crisp. Bake for 35-40 minutes until the potatoes are golden and set; this pre-baking prevents a soggy crust.
While the crust bakes, heat a skillet over medium-high heat and add a light coating of oil. Add the diced chicken thighs and cook for 4-5 minutes, stirring occasionally, until they begin to brown on the edges. Add the chopped onion and minced garlic, continuing to cook for another 3-4 minutes until the onion is softened and the chicken is cooked through. The chicken should be no longer pink inside and the aromatics should be fragrant. Set the pan aside to cool slightly.
In a blender, combine the room-temperature eggs and cottage cheese, blending until completely smooth—this ensures a creamy, even custard without lumps. Pour the blended mixture into a bowl and stir in the grated parmesan cheese, salt, pepper, nutmeg, and red pepper flakes until well combined. I like to taste a tiny bit at this point to adjust the seasoning if needed, as you won't be able to adjust it once it's baked. Add the fresh spinach to the cooled chicken mixture from Step 2, stirring to combine; the residual heat will slightly wilt the spinach while keeping it vibrant.
When the potato crust has finished baking and is golden, remove it from the oven and lower the oven temperature to 180°C (350°F). Spread the chicken and spinach mixture evenly over the bottom of the crust, then pour the egg custard from Step 3 over the top, making sure it's distributed evenly and fills all the gaps. Bake for 40 minutes until the custard is set but still slightly jiggly in the very center—it will continue cooking as it cools, and overbaking makes it rubbery. The top should be lightly golden.
Remove the quiche from the oven and let it rest for 10 minutes before slicing—this allows the custard to fully set and makes for cleaner slices. Slice into wedges and serve warm or at room temperature with your favorite sides.