Spread refried beans in the bottom of a casserole dish. Mix together sour cream and taco seasoning and spread mixture on top of refried beans.
Combine mashed avocados, salt, lime juice, mayo, cumin, and garlic powder and mix well (it can still be chunky). Spread guacamole on top of sour cream mixture.
Sprinkle black beans evenly on top of guacamole. Sprinkle Mexican style cheese on top of black beans. Then sprinkle pepperjack cheese on top.
Top with green onions, white onions, tomatoes and cilantro. Cover and chill until ready to serve. Serve cold or at room temperature with tortilla chips.
Notes
Store covered tightly in fridge up to 24 hours before serving.