In a small saucepan, cover the quinoa with the water and bring to a boil. Cover and cook over moderately low heat until the water has been absorbed and the quinoa is tender, about 15 minutes. Uncover, fluff the quinoa and transfer to a large bowl.
Meanwhile, light a grill. Grill the dates over moderate heat until lightly charred and very soft, about 2 minutes. Transfer the dates to a shallow bowl and mash to a puree with a fork. Stir in the vinegar and season the puree with salt.
Grill the fava bean pods over moderately high heat, turning, until the pods are softened and hot within, about 5 minutes. Transfer the pods to a bowl, cover with foil and let steam for 5 minutes.
In a small bowl, stir the lemon zest, juice and olive oil and season with salt and pepper. Shell and peel the fava beans and toss them with 1 tablespoon of the dressing.
Brush the scallions and green garlic with some of the dressing, season with salt and pepper and grill over moderately high heat, turning, until browned and tender, about 2 minutes. Transfer the scallions and green garlic to a work surface and cut them into 2-inch lengths.
Mix the fava beans, scallions, green garlic and mint into the quinoa. Add the remaining dressing and toss well. Season with salt and pepper. Spread the date puree on the bottoms of 4 plates and spoon the quinoa salad on top. Garnish with the sorrel leaves and serve.