Rinse the quinoa and add to a medium pot with the water. Heat until boiling. Turn heat to low/simmer, cover the pot with a lid and cook for ~ 15 minutes or until quinoa is light and fluffy.
While the quinoa is cooking, finely chop the red onion and lightly chop the arugula.
Add the warm cooked quinoa to a large mixing or serving bowl. Add the arugula, frozen peas, feta cheese, pine nuts, and onion. Stir ingredients. Add the vinaigrette, salt, and pepper to your taste and toss well.
Allow to cool to room temerature or chill in the refrigerator before serving. You can make the quinoa arugula salad ahead of time and store it in an airtight container in the refrigerator for 2-3 days.
Notes
Low FODMAP option: Omit red onion and green peas.
Grain substitutions: swap the quinoa with rice, sorghum, fonio, or buckwheat.
Cheese substitutions: try goat cheese instead of the feta or omit it for a vegan version.
Pine nut substitutions: sunflower seeds or almonds