Step 1

Preparation Bring quinoa, 1/2 teaspoon salt, and 1 1/4 cups water to a boil in a medium saucepan over high heat. Reduce heat to medium-low, cover, and simmer until quinoa is tender, about 10 minutes. Remove from heat and let stand, covered, for 5 minutes. Fluff with a fork.

Step 2

Meanwhile, whisk lemon juice and garlic in a small bowl. Gradually whisk in olive oil. Season dressing to taste with salt and pepper.

Step 3

Spread out quinoa on a large rimmed baking sheet; let cool. Transfer to a large bowl; mix in 1/4 cup dressing. DO AHEAD: Can be made 1 day ahead. Cover remaining dressing and quinoa separately; chill.

Step 4

Add cucumber, tomatoes, herbs, and scallions to bowl with quinoa; toss to coat. Season to taste with salt and pepper. Drizzle remaining dressing over.