Thaw fish, if frozen. Rinse fish; pat dry with paper towels. Cut into serving size pieces, if necessary. Set aside.
For brushing sauce, combine melted margarine or butter, onion salt, marjoram, and the 1/4 teaspoon thyme.
Place fish steaks on the rack of an unheated broiler pan. Brush fish steaks with brushing sauce. Broil 4 inches from the heat for 5 minutes. Turn fish. Brush with remaining brushing sauce. Broil for 3 to 7 minutes more or until fish flakes easily with a fork.
Meanwhile, for Dijon sauce, in a small saucepan stir together the sour cream, flour, mustard, salt, pepper, and the 1/8 teaspoon thyme. Add chicken or vegetable broth, stirring until well mixed. Cook and stir over medium heat until mixture is thickened and bubbly. Cook and stir for 1 minute more. Keep warm.
Toss together spinach and carrot. Line individual plates with the spinach mixture. Serve fish on spinach mixture. Top with Dijon sauce. Garnish with lemon wedges, if desired. Makes 4 servings.