In a saucepan, heat olive oil and saute the chopped garlic and onion over high heat until tender. Reduce the heat to mediumlow and add the bell pepper, shrimp or chicken stock, tomatoes and remaining seasonings. Simmer the sauce approximately 25 30 minutes until reduced and thickened. Ladle the sauce lightly over the catfish fillets and garnish with sprigs of thyme. The sauce is also excellent over white or brown rice as a side dish or vegetarian treat.