This is a Baja California style ceviche, where you marinate the clams in a mix of lime and tomato juice, or V8 Spicy Hot if you like. You can use fish instead of clams, too.
Mix together the V8 or tomato juice, lime juice, clam juice, Worcestershire sauce and Maggi, if using. Mix in the minced shallot and clams, chiles and oregano. Let this steep in the fridge for 30 minutes.
Mix in the remaining ingredients and serve with tortilla chips or on tostadas.