Season the chicken with garlic powder, onion powder salt and black pepper to taste.
Heat the olive oil in a large skillet over medium heat.
Add the chicken and cook for 5-6 minutes per side or until browned.
Remove the chicken from the skillet.
Add the chopped onion and minced garlic to the skillet and cook for 1-2 minutes.
In a large measuring cup combine the chicken stock, milk, arrowroot flour, mustard and nutritional yeast.
Season to taste with salt and black pepper.
Add the mixture to the skillet and stir to combine.
Return the chicken to the skillet.
Simmer for 10-15 minutes, stirring frequently or until thicken.
Add the spinach and chopped dried tomato and simmer until spinach is wilted and tomatoes are softened.