Bring the water for a boil in a medium saucepan over high heat. Add the amaranth and reduce to a simmer. Cover and cook for 15-20 minutes or until nearly all of the liquid is absorbed. Remove from heat and transfer to a large mixing bowl. Spread into an even layer and allow to cool.
While the amaranth is cooling, slice the cucumber in half. Using a spoon, scoop and scrape to remove the seeds. Slice into strips, then dice. Finely dice the red onion and chop the herbs. Add the veggies, herbs, and all other ingredients to the mixing bowl with the amaranth once it reaches room temperature. Mix well.
Add the cheese and toss gently. Serve immediately or chill for 30-60 minutes if desired. Store in the refrigerator for 3 to 5 days.
Notes
If desired, toast the pine nuts before adding to the mixture for additional flavor. If you need the amaranth to cool more quickly, place in a fine mesh sieve and rinse with cold water until it reaches room temperature. It may also be cooked ahead of time if needed.Cherry tomatoes may be halved or whole, depending on their size.