Quinoa: Rinse the quinoa in a fine-mesh sieve under cold water. Add it to a saucepan with double the volume of water and a pinch of salt. Bring it to a boil. Reduce to low-medium heat and simmer until most of the water has been absorbed. Then, remove from the heat, cover with a lid, and let it sit for 10 more minutes. Let cool completely.
Fruits: Wash the fruits. Cut the cherry tomatoes into quarters. Cut the peaches in half, remove the pits, and cut them into small dice or slices. Pit the avocado and score it lengthwise, then crosswise. Scoop out the pieces with a tablespoon.
Dressing: Add the olive oil, red wine vinegar, raspberries, shallot (if using), mustard, salt, and pepper to a blender. Blend until perfectly smooth.
Assembly: Add the spring mix, cooled quinoa, peaches, cherry tomatoes, and avocado to a large mixing bowl. Save some peach slices. Toss with half of the dressing. Transfer to individual plates and garnish with the peaches, sunflower seeds, and more dressing.
Notes
Cook your quinoa in vegetable broth (or add vegetable broth powder to the cooking water) for added flavor (trust me this makes all the difference).
Make the quinoa ahead of time and let it cool down completely for a crisp and cold salad. I like to make it the day before or even use leftover quinoa from another recipe.
Dry-roast the sunflower seeds for added flavor. Simply toast them in a pan without oil over medium-high heat until golden. Stir often and watch carefully to prevent them from burning.
Storage tips: If making the salad ahead of time, store the chopped-up fruits and greens, the quinoa, and the dressing in separate airtight containers in the refrigerator for up to two days. Assemble it shortly before serving to prevent it from getting soggy. If you have leftovers, try to eat them within 24 hours and keep the remaining vinaigrette in a separate container.