Trim the leaves from the broccoli and rinse. Cut stems and flowerets into bite-sized pieces. Cut stems from mushrooms, and cut mushrooms into 1/4-inch slices. If the scallops are larger than 1 inch in diameter, cut each in half. Rinse and pat dry with paper towel. Drain the pimientos in a strainer.

Melt margarine in a 3-quart saucepan over medium heat. Cook the mushrooms in the margarine about 5 minutes, stirring frequently, until tender when pierced with a fork. Stir in the scallops, broccoli and pimientos. Cook 3-4 minutes, stirring frequently, until scallops are white. Remove pan from heat.

Gradually stir the chicken broth into the cornstarch until the mixture is smooth. Stir the broth mixture and soy sauce into the scallop mixture. Heat to boiling over high heat, stirring constantly. Continue boiling 1 minute, stirring constantly. Serve over rice.