(1) Rinse the quinoa in 3 changes of water in a bowl, rubbing the grains and letting them settle each time before pouring off the water (if the quinoa does not settle, drain in a large fine-mesh sieve after each rinse). (2) Cook the quinoa in a medium saucepan of boiling well-salted water until tender, about 15 minutes. Drain well in a sieve and let cool. (3) Combine the chickpeas, spinach, tomatoes, scallions and cooled quinoa in a large bowl. Add the feta, lemon juice and olive oil and toss gently but thoroughly to combine. Season to taste with salt and pepper.