Preheat the oven to 400°F. Generously grease the bottom, corners, and sides of a 9×13-inch baking dish.

Add the chicken broth and 1/2 cup milk to a medium saucepan and bring them to a gentle simmer. In a small bowl, whisk the remaining 1/2 cup milk with the poultry seasoning and flour until completely smooth. Gradually whisk a small amount of the warm broth mixture into the flour mixture, then slowly return it to the saucepan. Cook while whisking until the sauce is smooth and lightly thickened.

In a large mixing bowl, combine the prepared sauce, 1 cup water, rinsed quinoa, and optional turkey bacon. Stir until the grains are distributed evenly, then pour the mixture into the prepared baking dish.

Cut the chicken breasts into thin, evenly sized strips. Arrange them in one layer over the quinoa mixture and sprinkle the all-purpose seasoning evenly over the top.

Bake uncovered for 30 minutes. While the casserole cooks, bring a saucepan of water to a boil, blanch the broccoli for 1 minute, and immediately rinse it under cold water. Leave the broccoli in a colander to drain.

Remove the casserole from the oven and carefully stir the quinoa mixture around the chicken. Check the thickest chicken strips with an instant-read thermometer. If the quinoa is firm, the sauce remains very loose, or the chicken has not reached 165°F, continue baking uncovered for 10–15 minutes.

When the quinoa is tender and the chicken is fully cooked, fold in the drained broccoli. Add some of the remaining water only as needed, up to 1 additional cup, until the mixture is creamy and easy to stir.

Sprinkle the Gruyère evenly over the casserole. Bake for about 5 minutes, or until the cheese has melted. Remove the dish from the oven and let it rest for 5–10 minutes before serving.