Begin by heating the olive oil in a large skillet over medium-high heat. Once shimmering, add the chopped onions, celery, and mushrooms. Sauté until tender, about eight minutes.
Add the minced garlic and dried thyme to the skillet. Stir for about one more minute until fragrant.
Pour the quinoa into a fine mesh sieve and rinse it well under cold water to remove bitterness.
Add the rinsed quinoa to the skillet with the sautéed vegetables. Pour in the vegetable broth, salt, and pepper. Bring to a boil.
Reduce heat to low, cover, and cook for about fifteen minutes until quinoa is tender.
If needed, let it sit covered for an additional ten minutes to finish cooking.
Remove the lid and fluff the quinoa with a fork. Adjust seasoning to taste.
If using, stir in the pecans for added crunch.
Serve warm or store leftovers in an airtight container in the fridge for up to five days.