Combine the dry spices in a small bowl
Add mushrooms to a large mixing bowl, coat and toss with oil, vinegar and soy sauce
season the mushrooms with the spice mix and massage to coat thoroughly
Saute the mushrooms in 2 batches in a large heavy bottom skillet. Saute on medium-high for 5-8 minutes a batch until fragrant and darkened.
After mushroom batches are cooked, return all to pan with the spinach and onion
cover and steam for 2 minutes, uncover, toss to combine and steam another 2 minutes
uncover and simmer another 4 minutes to reduce liquid
remove the filling from the pan with a slotted spoon, discard the remaining juices