Preheat the oven to 350°F.

Bring the water to a boil in a Dutch oven or large, oven-safe pot over high heat. Add the salt followed by the chicken tenders and boil, uncovered, until mostly cooked through, about 10 minutes.

Add the celery and onion to the pot, then reduce the heat to medium-low to maintain a simmer, cover with a lid, and cook until the vegetables are mostly tender, another 10 minutes.

Use tongs to remove the chicken from the pot and set it aside. Add the rice to the pot with the water and vegetables, cover, and simmer until the rice is cooked through, about 20 minutes.

Remove the pot from the heat and gently stir the rice to make sure all the liquid is incorporated. If the rice is fully cooked but seems a little watery, drain the leftover liquid before proceeding.

Add the shredded chicken and soup and stir to combine. Taste, adding salt if needed, then smooth the mixture into an even layer.

Bake, uncovered, until the top is set and lightly golden, about 30 minutes. If you want a crustier top, broil for 2 to 4 minutes until the top is golden brown.

Allow to cool slightly, about 5 minutes. Sprinkle with pepper, if desired, and serve.

Leftovers can be stored in an airtight container for 3 to 4 days in the refrigerator and also freeze well.