Prep Mushrooms: Start by cleaning the button mushrooms thoroughly. Slice them into even pieces, coat with flour and a pinch of salt, and let them sit to absorb the seasoning.

Fry Mushrooms: Heat oil in a deep frying pan over medium heat. Fry the coated mushrooms in batches until they're golden and crispy, about 4-5 minutes. Drain them on paper towels.

Make Sauce: In a wok, heat a little oil and sauté minced garlic and sliced green chilies until fragrant. Then, toss in cubed onions and capsicum, stir-frying for 2-3 minutes.

Combine Ingredients: Pour in the soy sauce, red chili sauce, ketchup, and vinegar. Stir well and then mix in a cornflour slurry.

Toss Mushrooms: Lower the heat and gently add the fried mushrooms to the sauce, tossing them to coat evenly. Adjust with water if the sauce is too thick.

Garnish and Serve: Sprinkle chopped spring onion greens on top and serve hot.