Heat the oil in a medium nonstick saucepan over medium- high heat. Add the onion and celery, sprinkle with salt and pepper, and cook, stirring often, until the vegetables are somewhat softened, about 4 minutes.
Add the cubed chicken and cook, stirring, for 2 minutes. Pour in the broth, and add the tarragon and quinoa. Bring to a simmer, reduce the heat to low, and cook, stirring occasionally, until the quinoa is tender, 12 to 15 minutes.
In a small bowl combine the lemon juice and cornstarch and add to the stew. Allow to cook at a low simmer while stirring for 2 minutes while mixture thickens. Taste for seasoning and serve immediately.
For a twist, try replacing the chicken with cooked shrimp (as depicted in the image). Simply add 1 tablespoon of butter to a non-stick frying pan and fry on medium heat for about 4-5 minutes. Be sure to remove the tails prior to cooking.