In a small bowl, stir together orange juice, hoisin sauce, vinegar, ketchup, and 3/4 teaspoon salt; set sauce aside. Cut off tops 1 to 2 inches below florets. Trim broccoli and discard tough ends of stalks, then peel and thinly slice crosswise. Separate broccoli heads into florets.
In a large pot of boiling salted water, cook noodles until al dente according to package directions, adding broccoli (stalks and florets) and peas during last minute of cooking. Drain; transfer to a large bowl.
In a large skillet, heat oil over medium heat. Dredge pork in cornstarch, shaking off excess. Saute pork until lightly browned and cooked through, tossing frequently, about 3 minutes. Pour in reserved sauce, and bring to a boil. Add to bowl with noodles; toss to combine.