Combine chicken, spinach, 2 Tbsp of taco seasoning, cumin, garlic powder, and red onion in a large bowl. Season with pepper and taste. Add additional taco seasoning, if desired. Season with salt as needed.
In a separate small bowl, combine sour cream and chili verde salsa. Taste, and season with salt, pepper, taco seasoning and/or cumin as desired.
Smear approximately 1/4 cup of the creamy salsa mixture all over the bottom of a 9×13 glass baking dish. Mix approximately 1/2 cup of the creamy salsa into the chicken and spinach mixture. Add more creamy salsa, 1 tablespoon at a time, if the mixture is dry. You want it to be a moist mixture, but not goopy and saturated.
Measure 1/4 cup of the chicken mixture into the center of a tortilla and roll up. Place tortilla at one end of the baking dish, seam down. Repeat with remaining tortillas and chicken mixture.
Spread the remaining creamy salsa mixture over the enchiladas. Sprinkle with shredded cheese and bake in the oven for about 20 minutes, or until the cheese is melted and slightly bubbly.
*See substitution ideas for notes on the tortillas.