Combine Cottage cheese, tomato, celery, dill weed, salt and mustard in small bowl; stir until well blended.
Close and secure ends of each trout steak with toothpicks to form pockets.
Fill pockets with Cottage cheese mixture.
Melt butter in large skillet over medium heat until hot and bubbly.
Add trout steaks; cook 10 to 15 minutes until fish flakes easily with fork, turning once.