Cut the gai lan leaves from the stems. Cut the stems crosswise into ¼-inch-thick pieces; place in a small bowl. Stack the leaves and cut crosswise into 1-inch-wide pieces; set aside.  Place the soy sauce, brown sugar, and Sriracha in a small bowl and stir until the sugar dissolves; set aside.  Heat 1 tablespoon of the oil in a large nonstick frying pan or wok over medium-high heat until shimmering. Add the mushrooms, sprinkle with ½ teaspoon of the salt, and cook, stirring rarely, until browned around the edges, about 3 minutes. Transfer the mushrooms to a medium bowl.  Heat the remaining tablespoon of oil in the same pan over medium heat until shimmering. Add the reserved gai lan stems, onion, garlic, and remaining ½ teaspoon salt and cook until the onions have softened, about 5 minutes.  Add the reserved gai lan leaves, rice, and cooked mushrooms and cook, stirring occasionally, until the leaves just start to wilt and the mixture is heated through, about 4 minutes. Add the reserved soy sauce mixture and stir to combine.  Push the rice mixture to one side of the pan, add the eggs, and cook, stirring occasionally with a rubber spatula, until almost set, about 2 minutes. Season to taste with salt. Remove the pan from heat, sprinkle with the scallions, and toss to combine. Serve immediately.