1. Combine soy sauce, peanut butter, brown sugar, cumin, sesame oil, red pepper flakes and garlic in a bowl and whisk until smooth.
2. Pour mixture into an 11x7x2-inch microwave-safe pan.* Add swordfish and turn to coat both sides. Marinate for 15 minutes.
3. Turn steaks over and cover with microwave safe lid or wax paper.
4. Microwave on HIGH for 1½ minutes then rotate the dish ¼ turn.
5. Sprinkle with onions and continue to microwave on HIGH 1½ minutes longer or until fish flakes easily when tested with a fork.
6. Let stand, covered, for 2 minutes brfore serving.
*If you prefer not to microwave the steaks, after they are marinated place them on a grill or broiler for 6 minutes on one side then flip, baste and cook the other side for 5 minutes. Add onions and cook for an additional 1 - 2 minutes. Onions should be browned, not burned.