In a large mixing bowl, whisk together the Mushroom Coating ingredients: all purpose unbleached flour, garlic powder, onion powder, salt and pepper. Dust mushrooms several at a time. Set aside.
In a large mixing bowl, mix together the ingredients to create Mushroom Batter: all purpose unbleached flour, cornstarch, garlic powder, baking powder, salt, pepper and water. Mix batter until well combined and set aside.
Heat the oil in a pot or a deep fryer over medium-high heat. Test to see if oil is hot by frying a drop of batter.
Dip mushroom into the batter and drop it into the hot oil. Fry several at a time until each side is golden brown, about 3-5 minutes. Remove with a slotted spoon and strain excess oil on a paper towel.
In a wok, add 1 tbsp of avocado oil. Fry onions, bell peppers and pineapples until soft. Remove from wok and set aside.
In a medium bowl, mix together the Sauce ingredients: canned pineapple juice, cornstarch, water, vinegar, ketchup and soy sauce. Pour into a sauce pan and let it come to a boil, reduce heat and simmer until sauce has thickened. Add back in the cooked vegetables and pineapple. Mix and pour your sauce over the battered mushrooms.
Serve with steamed rice and enjoy!