Rinse and drain quinoa. Add to a medium saucepan and bring water and quinoa to a boil. Reduce to a simmer, cover, and cook for 10-15 mins. Use a fork to fluff the quinoa and let cool for 5-10 mins.
In a medium bowl, stir together the cooked quinoa, spinach, tomatoes, red onion, and feta.
In a small bowl, whisk together the lemon juice, olive oil, salt, and pepper.
Gently stir through the avocado and top with the lemon dressing. Enjoy!