1. In a large skillet, toast the cumin seeds over moderate heat until fragrant, about 1 minute. Transfer the seeds to a plate to cool, then coarsely chop them.
2. Preheat the oven to 350°. Heat the olive oil in the skillet. Season the fish with salt and lots of pepper. Add the fish to the skillet and cook over moderately high heat until browned on the bottom, about 3 minutes. Turn the fish and continue cooking over moderate heat until barely opaque throughout, about 4 minutes longer. Transfer the fish to a plate.
3. Add the onion to the skillet, cover and cook over low heat until softened but not browned, about 5 minutes. Add the cumin and olives and cook, stirring to blend the flavors. Return the fish to the skillet and gently break it up with a wooden spoon. Season with salt and pepper.
4. Warm the tortillas in the oven for 30 seconds, or just until hot but still pliable. Keep the tortillas warm in foil. To serve, toss the lettuce with the tomatoes and cucumber in a bowl. Transfer the fish mixture to another bowl. Set out the sour cream and hot sauce. Let guests build their own tacos with the fish, salad, sour cream and hot sauce.
Wine Recommendation: Contrast the oily fish with a simple, cleansing Spanish white, such as the 1998 Torres Chardonnay Viña Sol or the 1997 Marqués de Cáceres Blanco.
Notes: One Serving: Calories 412 kcal, Total Fat 22 gm, Saturated Fat 5 gm