Spread mashed avocados on the bottom of a platter or low-line bowl. Lightly salt to taste.
Mix the Greek yogurt with taco seasoning and spoon/spread it carefully over the avocados.
Lightly layer the beans on top of the yogurt, and then spread the corn.
Sprinkle chopped romaine lettuce on top of the beans and corn.
Sprinkle with cheese, and garnish with diced tomatoes. Serve.