Rinse the quinoa thoroughly to remove any bitterness, then cook it as per the instructions on the package.
Prepare the dressing by combining lemon juice and zest, oregano, salt, and pepper in a large bowl. Gradually whisk in the olive oil until well blended. Adjust the flavors to your taste.
Mix the cooked quinoa with the dressing in the bowl, ensuring it's fully coated. Let it cool to allow the flavors to meld.
Chop the scallions, bell peppers, and cucumber, and halve the olives. Gently fold these fresh veggies into the cooled quinoa.
Top the salad with crumbled feta cheese and give it a final toss before serving. Enjoy this delightful salad at room temperature or chilled.