Coat a casserole dish (capacity 700 ml) with water and spread with cling film. Dry the olives. Cut peppers into small pieces, put half aside for garnish. Soak gelatin in cold water.
Break up cream cheese and stir through with sour cream. Heat a small amount over steam. Squeeze gelatin and let it melt in it. Stir well with the remaining amount. Stir in bell pepper pieces and olives. Season with salt, pepper and oregano, fill into the mold and spread evenly. Cover with plastic wrap and cool for about 10 hours to set.
Turn terrine out of mold, remove plastic wrap and cut terrine into slices. For garnish, shred leaf lettuce, rinse and drain well. Serve terrine garnished with olives, lettuce, olive oil and remaining bell pepper pieces.