In large pot, heat oil over medium heat. Add the onion, oregano, and garlic. Saute for about 5 minutes, stirring often, until onion is softened.

Add the broth, increase heat to medium-high, and bring to a boil.

Add the chicken and boil until it is cooked through, about 7-10 minutes. (If you are using large pieces of chicken, I recommend cutting each piece in half to help it cook faster.) Transfer the cooked chicken to a plate and set aside.

Add tomatoes, squash, and quinoa to the pot. Reduce heat and simmer for about 15 minutes, until the squash is tender and the quinoa is cooked. If desired, mash up some of the squash pieces.

Shred the chicken and return it to the pot. Stir in the salt and pepper. Add more to taste, if needed.

Stir in the chopped fresh spinach and cook for 1-2 minutes until it is wilted. Serve warm.

INSTANT POT:
Set Instant Pot to saute and add the oil. Once oil is hot, add the onion, oregano, garlic, and chicken (uncooked and diced); saute, stirring often, until onions soften, about 5 minutes. Then add the broth, tomatoes, squash, and uncooked quinoa. Cook for 5 minutes at high pressure, until squash is tender, chicken is cooked through, and quinoa is cooked. Use Natural Pressure Release for 2-3 minutes, and then use a Quick Pressure Release. Add salt and pepper, to taste. Add spinach and stir for a minute or two, until wilted. Serve warm.