Remove the skin from the avocados.
In a bowl, mash avocados and combine with lemon juice, garlic and salt until well mixed. Set aside for the 2nd layer.
In another bowl, combine sour cream, chili powder, salt and cumin until well mixed. Set aside for 3rd layer.
Spread one layer at a time on a large, flat plate or dish.
Add mild taco sauce or salsa to the top if desired.
Serve with tortilla chips