To a large pot, add a fat pinch salt and the potatoes. Cover the potatoes with water, and bring to a boil. Cover, and lower heat to a simmer. Let the potatoes cook until tender when pierced with a sharp knife, about 15 minutes. Drain potatoes and let them cool until ready to handle.

Preheat oven to 450°F and prepare 2 baking sheets with parchment paper, and spray each one with a thin coating of avocado oil. One by one, place the potatoes on the baking sheets, and using the bottom of a large glass, press down lightly and smash them. Repeat with all the potatoes. Spray the tops and sides with more avocado oil, and sprinkle with flaky sea salt. Cook for roughly 20 minutes, until tops are lightly golden, then flip the potatoes over. Place back in the oven and cook for another 10-15 minutes, until edges are golden and crispy. Remove from oven and let cool for roughly 10 minutes.

Place potatoes on a large platter or a large shallow bowl. Drizzle over the garlicky yogurt vinaigrette, and add the pickled onions. If you want, give everything a light toss, just to cover the potatoes (add more vinaigrette, if needed), and top with the chopped herbs. Serve immediately.

Make the pickled onions: In a bowl, whisk together the water, vinegar, sugar, and salt until everything has dissolved. Place the sliced onions in a jar and cover with the pickling solution. Cover with the lid and store in your refrigerator for up to 1 week.

Make the vinaigrette: In a large bowl, whisk together the yogurt, oil, vinegar, mustard, maple syrup, and garlic. Season with salt and pepper. Taste and adjust if necessary. Vinaigrette can be stored in an airtight container in the fridge for up to 1 week.