1. Boil spinach according to package directions and drain well.
2. Preheat oven to 350 degrees.
3. In large skillet, cook onions,mushrooms and garlic in butter until tender.
4. Place cooked mushroom mixture in blender or processor and blend or process on high for 30 seconds or until mushrooms are finely chopped.
5. Place spinach, mushroom mixture, cream cheese,pepper-jack cheese, sour cream, Parmesan cheese, and spices in a large mixing bowl and mix well.
6. Pour spinach mixture into large baking dish.
7. Test for seasoning and adjust if needed.
8. Sprinkle with cheddar cheese and bake for 35 to 40 minutes or until golden brown.
9. Serve with tortilla chips, crackers, or toasted bread rounds.