Heat the olive oil in a large pot or deep skillet over medium-high heat.
Add the chicken pieces and cook for 5-6 minutes, stirring occasionally, until browned and cooked through. Remove the chicken from the pot and set aside.
In the same pot, add the diced onion and cook for 3-4 minutes until softened.
Add the minced garlic and sliced mushrooms to the pot and cook for another 4-5 minutes until the mushrooms are tender and have released their moisture.
Stir in the rinsed quinoa, chicken broth, dried thyme, dried oregano, salt, and black pepper.
Bring the mixture to a boil, then reduce the heat to low and cover the pot.
Simmer for 15 minutes, or until the quinoa is cooked and the liquid is absorbed.
Return the cooked chicken to the pot and stir in the fresh baby spinach.
Cook for an additional 2-3 minutes, stirring occasionally, until the spinach is wilted and the chicken is heated through.
Remove from heat and serve warm.