In a small bowl stir together the soy sauce, 3 tablespoons orange juice, sugar, ginger, and garlic. Coat the inside of a 4-quart slow cooker with cooking spray. Add the beef and the soy sauce mixture; stir to combine. Cover and cook on low-heat setting for 6 hours.
Just before beef is done, place broccoli in a medium microwave-safe bowl. Cover bowl with waxed paper. Cook on 100% power (high) for 4 minutes; drain off any liquid. Using a slotted spoon, transfer beef to a large bowl. Use the spoon or 2 forks to break up the beef into smaller pieces. Add the broccoli to the bowl. Cover to keep warm and set aside.
Place a small fine mesh sieve over a small saucepan. Pour the juices from the slow cooker into the pan. In a small bowl stir together the cornstarch and 2 tablespoons water. Add to saucepan. Cook and stir until slightly thickened and bubbly. Cook and stir 2 minutes more. Remove from heat. Stir in orange marmalade, remaining 1 tablespoon orange juice, and pepper to taste.
Add about half of the sauce and cashews to the beef and broccoli mixture; toss to coat. Serve over hot cooked rice or noodles; pass remaining sauce.