Preheat oven to 375 degrees F. Bring 1 cup of vegetable broth to a boil in a medium-sized saucepan, then add in the quinoa and stir together until thoroughly combined.

Bring quinoa to a boil, then reduce heat to low, cover the pan and simmer covered for 10 minutes. After the 10 minutes are up, turn the burner off and leave the pan sitting there covered for another 10 minutes (DO NOT lift the lid during this time). When the quinoa's 10-minute sitting time is done, uncover and fluff with a fork.
Note: The quinoa may not look fully done to you. This is fine, as it continues to cook later in the oven and ends up the perfect consistency.

Heat the olive oil in a medium-sized saute pan over medium heat. Add the celery and cook until it is still slightly crunchy but has softened a bit (about 2-3 minutes). Turn the burner off, then add in the sage and 1/2 cup of the remaining vegetable broth and stir to mix everything together.

Add the celery mixture, poultry seasoning and the remaining 1/2 cup of vegetable broth to the quinoa and stir together well until thoroughly combined. Taste test quickly for salt levels and add salt to taste, if needed (usually, the amount of salt needed depends on what kind of broth you use as well as your salt-level preference).
Note: It may seem super liquidy to you. This is fine, as the quinoa continues to cook in the oven and the moisture is absorbed into the quinoa.

Place the stuffing mixture into a greased baking dish (I used a 2.5 quart oval baking dish). Bake on rack in the center of the preheated oven for 10 minutes. Then, remove from oven and fluff up a bit with a fork. Increase oven temperature to 500 degrees F, move the rack up to the top of the oven, place quinoa back in the oven and cook for ~8-10 minutes until the top of the stuffing becomes golden brown.

Remove from oven and serve immediately. Store leftovers in an air-tight container for up to 5 days in the refrigerator (if they last that long!).