03Heat remaining 1 1/2 tablespoons oil in a 12-inch heavy skillet over moderately high heat until hot but not smoking, then sauté bell peppers, stirring, until just tender, 6 to 8 minutes.
04Spread potato slices evenly in an oiled 13- by 9- by 2-inch glass baking dish and season with salt and pepper. Top with peppers, then tomatoes and fish, seasoning each layer with salt and pepper. Sprinkle fish with lemon juice.
05Purée all sauce ingredients except oil in a food processor or blender. With motor running, add oil in a slow stream.
06Pour sauce evenly over fish and bake in middle of oven until fish is just cooked through, 25 to 30 minutes.