In a large pot, bring the water and bouillon cubes to a rolling boil over medium-high heat.
Add the optional carrots and celery, followed by the raw boneless chicken thighs. Reduce heat, cover, and simmer for 25-30 minutes until the chicken is tender.
While the chicken cooks, lightly dust a clean counter with flour. Take 5 canned biscuits, dust them lightly with flour, salt, and pepper, and stack them on top of each other.
Using a rolling pin, roll the stack of 5 biscuits out flat.
Use a pizza cutter to slice the flattened dough into small, bite-sized squares. Repeat with the remaining biscuits. Leave the excess flour on the dough.
Remove the cooked chicken from the pot, shred it with two forks, and return it to the broth.
Bring the broth back to a gentle boil. Drop the cut dumplings into the pot a handful at a time. Gently push them down with a spoon (do not stir vigorously).
Let simmer uncovered for 15-20 minutes until the dumplings plump up and the excess flour thickens the broth.
Remove from heat, stir in the optional green onions for color, and let cool for 10 minutes before serving.