Catfish Jambalaya

2 cups chopped onion
1/2 cup chopped celery
1/2 cup chopped green pepper
2 garlic cloves, minced
1/4 cup butter or margarine (optional)
1 (10 ounce) can diced tomatoes and green chiles, undrained
1 cup sliced fresh mushrooms
1/4 teaspoon cayenne pepper
1/2 teaspoon salt (optional)
1 pound catfish fillets, cubed
Hot cooked rice (optional)
Sliced green onions (optional)

In a saucepan over medium-high heat, saut