In a bowl, add 1 tablespoon cornstarch, 3 tablespoons flour, and ½ teaspoon black pepper. Add water a little bit at a time while stirring until a thick batter is formed.
In a pan on high heat, add 1 cup of vegetable oil and heat.
Coat the mushrooms on each side with batter. Deep fry the mushrooms in the hot oil for 8 minutes, flipping the mushrooms over halfway.
In a medium bowl, add 5 cloves of crushed garlic, ½ teaspoon chili flakes, 2 teaspoons ginger, 2 tablespoons soy sauce, ½ tablespoon rice wine vinegar, 1 tablespoon sriracha, and 1 teaspoon brown sugar. Mix well.
In a nonstick pan, add the mushrooms and sauce. Cook on high heat and stir well for 2 minutes.
Plate with rice and garnish with red chili, sesame seeds, and green onions.