Step 1

Heat a medium saucepan over medium-high. Swirl in 2 tablespoons oil. Add onion and garlic; season with salt and pepper. Cook, stirring occasionally, until onion is translucent, 3 to 4 minutes. Transfer onion mixture to a large bowl.

Step 2

Return saucepan to medium-high heat; add quinoa, 1/2 teaspoon salt, and 1 1/2 cups water. Bring to a simmer, then reduce heat to low and cook, covered, until water is absorbed and quinoa is tender, 14 minutes. Remove from heat; let stand, covered, 10 minutes. Fluff with a fork; add to bowl with reserved onion mixture. Let cool to warm room temperature, 15 minutes.

Step 3

Meanwhile, combine tomatoes, bell pepper, cucumbers, olives, vinegar, and remaining 1/4 cup oil. Season with salt and pepper. To serve, spoon quinoa onto plates and top with tomato mixture, feta, herbs, and pepperoncini. Drizzle with some dressing from bottom of bowl, if desired.