Boil a large pot of water. Add cauliflower and allow to par boil 2-3 minutes. Drain and set aside.
In a jar with a lid, combine stock, soy sauce, rice vinegar, sambal oelek, cornstarch, and fish sauce. Put lid on jar and shake well to combine.
Heat a medium skillet (cast iron works best) over medium-high heat. Add peanut and sesame oil. Add mushrooms and cook, turning, until starting to brown, about 2 minutes.
Add cauliflower and cook, stirring, until brown and fork tender, about 1 minute.
Shake jar one more time, and pour the sauce over cauliflower mushroom mixture.
Cook, stirring, until sauce is thickened and glossy, about 1 minute.
Remove from heat, and garnish with green onion.
Serve hot, with steamed rice or noodles
*Make this recipe vegan, by leaving out the fish sauce. Instead, taste and add salt to desired salt level, or use a vegan fish sauce, or Chinese cooking wine.*Tamari is gluten free, but if you are gluten free, there are soy sauces labeled as such. If not, they may contain gluten.