Preheat oven to 350 degrees F (175 degrees C). Lightly grease a medium baking dish.
In a medium bowl, mix the cayenne pepper, garlic powder, dill weed, thyme, salt, and pepper.
Brush catfish fillets with the margarine, and dip into the spice mixture to coat.
Arrange catfish fillets in the prepared baking dish, and bake 30 minutes in the preheated oven. Top with the partially drained diced tomatoes with green chile peppers, and continue baking 10 minutes, until fish is easily flaked with a fork.