Bring water to a boil and prepare a bowl of iced water. Add 1/2 of the parsley, 1/2 of the mint, and 1/2 of the tarragon. Blanch herbs for 5 seconds, then scoop into the iced water. Let cool completely, about 2 minutes. Drain well and squeeze out the water.

Rinse quinoa well. Sprinkle salt into the blanching water. Add the quinoa and simmer on medium heat until just barely tender, about 12 minutes.

Meanwhile, chop the remaining herbs into small pieces.

Add garlic to the blender with the blanched herbs. Squeeze in lemon juice and add olive oil. Blend starting on low speed, pulsing on and off, and finishing on high speed, until dressing is smooth and green.

Remove quinoa from heat; place in a strainer set over a bowl and drain for 5 minutes, tossing occasionally. Transfer quinoa to a bowl. Season with salt, black pepper, and cayenne pepper. Let cool until it is between warm and room temperature, 5 to 10 minutes.

Stir dressing into the quinoa. Continue cooling if salad is not yet at room temperature, 5 to 10 minutes more. Add the chopped herbs and mix to combine. Wrap bowl in plastic wrap and refrigerate until flavors meld, about 2 hours.

Taste the salad and adjust seasoning as desired. Transfer salad to a serving bowl.