Rinse quinoa under cold water, then combine with vegetable broth or water in a saucepan. Bring to a boil, reduce heat, cover, and simmer for 15 minutes. Let sit covered for 5 minutes, then fluff with a fork.

In a large bowl, combine cherry tomatoes, cucumber, bell pepper, spinach, red onion, and avocado. Add feta cheese if desired.

In a small bowl, whisk together olive oil, lemon juice, salt, and pepper to make the dressing.

Add the cooked quinoa to the bowl with the vegetables, drizzle with dressing, and toss gently to combine.

Garnish with fresh herbs and serve immediately or chill for later.