Beat softened cream cheese and sour cream together until completely smooth. Add taco seasoning and garlic powder and mix until fully combined and uniform in color. Taste and adjust — add a little more sour cream if it tastes too salty.
Spread the base evenly across the bottom of a wide shallow dish (9×13 inch or large round pie dish) going all the way to the edges. Use an offset spatula or back of a spoon for an even layer.
Warm refried beans in the microwave for 1 minute until spreadable. Spoon over the cream cheese base and spread gently and evenly. Let cool a few minutes before adding cheese.
Scatter shredded cheese evenly over the cooled bean layer. At this point the dip can be covered and refrigerated overnight if making ahead.
Within 1 hour of serving, add shredded lettuce, seeded diced tomatoes, diced green pepper, sliced black olives, and spring onions in that order. Spread each topping evenly to the edges.
Refrigerate for at least 30 minutes before serving. Serve cold directly from the dish with tortilla chips or Fritos scoops.
