Make salad dressing by putting mustard in a small bowl. While whisking, add balsamic vinegar. Whisk vigorously while streaming in olive oil to create an emulsion. Season with pepper and red pepper flakes. Preheat oven to 425 degrees. Mix together the lemon juice, dash of Worcestershire sauce in a small bowl and pour over salmon fillets. Let sit for no more than five minutes to marinate. Drain any excess liquid and press fillets into coriander seeds. Put fillets in oven and cook five minutes, or until desired doneness. While fish is cooking, toss spinach in dressing and place in a large bowl. Top with onions, mushrooms, walnuts and boiled eggs. Serve salmon with salad.