Make the dressing. Add the oil, lemon juice, mustard, honey, garlic, salt and pepper to a small bowl and whisk together until fully emulsified. Alternatively, you can add the ingredients to a small jar and shake together. Set aside.
Cook the quinoa. Add the quinoa and water to a medium saucepan over medium-high heat. Bring to a boil, then reduce the heat to a gentle simmer. Cook, covered, for about 15 minutes, or until the quinoa has absorbed all the water. Remove from the heat and allow the quinoa to steam, covered, for another 5 minutes. To cool the quinoa, spread it out on a baking sheet for about 15 minutes.
Make the salad. Once the quinoa is completely cooled, add it to a large mixing bowl with the bell peppers, cucumber, red onion, capers, parsley, and feta. Drizzle the lemon vinaigrette on top (you can use as much or as little as you'd like, though I tend to use it all).
Serve or chill. Serve the quinoa salad immediately or chill in the fridge to let the flavors meld together further.