Chicken
In a dutch oven over medium heat, add the chicken and stock.
Bring to a boil, then lower the heat, and simmer until the chicken is just done (~ 8-12 minutes). Transferred the cooked chicken to a large bowl
Strain the broth, reserving the liquid (Don't wash the Dutch oven, we'll use it again soon)
Meanwhile, adjust oven rack to upper-middle position and heat oven to 400° F
Filling
In the now-empty Dutch oven, warm 1 Tbsp oil over medium heat
Add the onion, celery, a strong pinch of sea salt and freshly ground black pepper
Cover and cook, stirring occasionally, until just tender (~ 5-7 minutes)
While the veggies are cooking, chop the chicken into bite-sized pieces
Transfer the cooked vegetables to bowl with chicken; set aside.
In the now-empty Dutch oven, warm 1 Tbsp oil over medium heat
Add the mushrooms, cover, and cook, stirring occasionally, until the mushrooms have released their juices (~ 5 minutes)
Add the soy sauce and tomato paste.
Increase the heat to medium-high and cook, stirring frequently, until liquid has evaporated, mushrooms are well browned, and dark fond begins to form on the surface of the pan (~ 5 minutes)
Transfer mushrooms to the bowl with chicken and vegetables. Set aside.
In the now-empty Dutch oven over medium heat, warm the butter.
When the foaming subsides, stir in the flour and cook (~ 1 minute)
Add the reserved chicken broth and slowly whisk.
Bring to a simmer, scraping the bottom with a wooden spoon to loosen the browned bits, then continue to simmer until the sauce has fully thickened (~ 1 minute)
Season to taste with sea salt and freshly ground black pepper.
Remove from the heat, add the lemon juice, and 2 Tbsp parsley.
Add to the sauce the chicken/veggie mix, along with the peas
Finish and Serve
Pour mixture into 13 by 9-inch baking dish or 4-5 mini cocottes and cover with tater tots.
Bake on rimmed baking sheet until filling is bubbling and the tots are well browned (~ 15 - 20 minutes)
Sprinkle with remaining tablespoon parsley and serve