Rinse quinoa in a fine-mesh strainer under cold water for 30 seconds to remove bitterness. Combine rinsed quinoa, water, and salt in a medium saucepan. Bring to a boil over high heat, then reduce to low, cover, and simmer for 15 minutes until water is absorbed. Remove from heat and let stand covered for 5 minutes. Fluff with a fork and spread on a plate to cool for 10 minutes.

In a small jar or bowl, combine olive oil, lemon juice, Dijon mustard, honey, minced garlic, oregano, salt, and pepper. Shake or whisk vigorously until emulsified and slightly thickened. Taste and adjust seasoning - the dressing should be bright and tangy.

In a large mixing bowl, combine cooled quinoa, baby spinach, chickpeas, diced cucumber, and red onion. The residual warmth from the quinoa will slightly wilt the spinach, which is exactly what you want.

Pour the dressing over the salad and toss thoroughly to coat every ingredient. Fold in the crumbled feta and toasted pepitas. Serve immediately, or refrigerate for up to 3 days - the flavors actually improve as they meld.