Step 1

Crumble the feta into a food processor fitted with the blade attachment and pulse several times to break it into very small pieces. With the machine running continuously, gradually pour in the water and oil and process for 30 seconds. Stop the processor and scrape down the sides of the bowl. Process again until smooth, about 30 seconds; set aside.

Step 2

Arrange a rack in the middle of the oven and heat to 425°F. Line a rimmed baking sheet with aluminum foil; set aside.

Step 3

Place the onion and 1 tablespoon of the lemon juice in a small bowl and toss to combine; set aside.

Step 4

Place the garlic, oregano, marjoram, pepper, 1 teaspoon of the salt, and the remaining 1/4 cup of lemon juice in a large bowl and stir to combine. Add the chicken and toss to coat. Place the chicken on the prepared baking sheet. Roast until the chicken is cooked through and registers 165°F on an instant-read thermometer, 18 to 20 minutes. Meanwhile, cook the quinoa.

Step 5

Place the quinoa, water, and remaining 1/2 teaspoon salt in a medium saucepan and bring to a boil over medium-high heat. Reduce the heat to low, cover, and simmer until the quinoa is tender and the water is absorbed, about 15 minutes. Remove the pan from the heat. Fluff the quinoa, cover again, and let stand for 5 minutes.

Step 6

To assemble, divide the quinoa between 4 bowls. Top each bowl with a chicken thigh. Divide the red onion, cucumbers, tomatoes, and olives between the bowls. Drizzle with the sauce and serve.