How to Make It
Place mushrooms and pork in a food processor; pulse 15 to 20 times or until finely chopped. Place pork mixture in a bowl with panko, 1/4 teaspoon salt, 1/4 teaspoon pepper, and egg; stir to combine. Divide and shape pork mixture into 24 meatballs (about 1 tablespoon each).
Heat 1 1/2 teaspoons oil in a large skillet over medium-high. Add Broccolini; cook 2 minutes. Place sautéed Broccolini in a bowl; set aside.
Add remaining 1 1/2 tablespoons oil to pan. Add meatballs; cook 5 minutes, turning to brown on all sides.
Combine 3/4 cup chicken stock, 1 tablespoon rice vinegar, brown sugar, soy sauce, and Sriracha in a bowl; add to pan. Cover, reduce heat, and simmer 3 minutes or until meatballs are done. Combine remaining 1/4 cup stock and cornstarch in a bowl; stir into meatball mixture. Cook 1 minute or until sauce is thickened.
Heat rice according to package directions. Stir rice, remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, and remaining 1 tablespoon vinegar into sautéed Broccolini. Serve with meatball mixture.