Preheat the oven to 425 degrees and line a baking sheet with parchment paper.
Add all of the potato ingredients to the baking sheet and toss to coat evenly. Spread in an even layer and place in the oven (on the center rack) for 15 minutes. Toss and place back in the oven for 10 more minutes, or until fork tender.
Meanwhile, add all of the dressing ingredients to a blender and blend until smooth. Taste and adjust the seasonings as needed. Set aside.
To assemble, add the quinoa, potatoes, onion, serrano, arugula & fresh herbs to a large bowl. Drizzle the dressing over and squeeze the lime juice. Toss until combined. Serve at room temperature or chilled.
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Notes
To make the quinoa, add 1 cup of rinsed, dry quinoa and 2 cups of liquid (broth or water) to a sauce pan. Bring to a boil, cover, lower the heat and simmer for 20 minutes. If you can make this ahead of time so that it is chilled by the time you add it to the salad, that is ideal.
If you want to add some extra protein to this, add in a can of rinsed white beans.