In a small bowl, mix mayonnaise, Mrs. Dash® Tomato Basil Garlic and Dijon mustard together and set aside. Heat grill to medium. Spray mushrooms lightly with cooking spray, sprinkle with Mrs. Dash® Steak Grilling Blend. Grill mushrooms 12-15 minutes turning once or twice until the mushrooms are brown and tender. If desired, grill buns until toasted. Spoon some sauce on top. Cover with top of bun and serve.