Preheat oven to 375. Clean mushrooms & remove stems. Place on baking sheet and put in oven for 20 minutes.
Mix diced cauliflower with remaining ingredients, crushing fried onions to resemble the texture of panko bread crumbs.
Remove mushrooms, notice they are filled with brown liquid. This is tasty! Add stuffing right on top, it will be absorbed. Stuffing should more than fill mushroom caps, making little round mounds. Sprinkle with salt and bake for another 10 minutes.