Crumble feta cheese into small bowl; mash in ricotta, lemon juice and oil until smooth. Stir in garlic and oregano. Blend in enough of the yogurt until of spreading consistency. Cover and refrigerate for at least 2 hours or up to 2 days. (Mixture thickens slightly when regrigerated.) Spoon mixture into mini pitas, spread it on slices of crusty baguette, or blend in more yogurt and serve as a dip for fresh vegetables.