Cook the Quinoa: Rinse 1 cup of quinoa under cold water. In a saucepan, combine with 2 cups of water and bring to a boil. Reduce heat, cover, and simmer for 12–15 minutes, until water is absorbed. Let it cool.
Prepare the Vinaigrette: In a small bowl or jar, whisk together the olive oil, lemon juice, Dijon mustard, garlic, honey, salt, and pepper. Taste and adjust seasoning.
Assemble the Salad: In a large salad bowl, combine cooled quinoa, chopped spinach, cherry tomatoes, red onion, cucumber, and herbs. Drizzle with vinaigrette and toss to coat evenly.
Add Feta and Serve: Gently fold in the crumbled feta cheese. Serve immediately or chill in the fridge for 15–20 minutes to let the flavors meld.