To cook the amaranth: Combine the rinsed amaranth and the water in a medium saucepan. Bring the mixture to a boil, then decrease the heat to low to maintain a very gentle simmer. Cook until the amaranth has absorbed all of the water, about 15 minutes, reducing heat as time goes on to maintain a gentle simmer. Remove from heat, cover, and let the amaranth rest for 5 minutes before mixing.
Cool the amaranth. You can do this quickly by spreading it out on a baking tray and placing it in the fridge or freezer for about 10 minutes.
In a large serving bowl, combine the chickpeas, cucumber, red bell pepper, red onion and parsley. Set aside.
In a small bowl, combine the lemon juice, vinegar, garlic and salt. Whisk until blended, then set aside.
Once the amaranth is mostly cool, add it to the serving bowl with the veggies, and drizzle the dressing on top. Toss until the mixture is thoroughly combined. Season with black pepper, to taste, and add an extra pinch of salt if necessary. For the best flavor, let the salad rest for at least 5 to 10 minutes before serving.
This salad keeps well in the refrigerator, covered, for about 4 days. Serve chilled or at room temperature.