In a small bowl, mix the sour cream and taco seasoning. In another small bowl, mix the mashed avocados, minced garlic, and mayonnaise.
In a small Pyrex dish or pie plate, layer the beans, sour cream mixture, avocado mixture, and salsa. Sprinkle the scallions on top.
Chill at least an hour, or until ready to serve. (The dip can be made a day ahead and kept, covered, in the refrigerator.)
To make the tombstones and tree, cut the shapes you want out of 2 large tortillas. Place the cut-out shapes on a parchment paper lined cookie tray and bake at 350 degrees until the tortillas are nice and brown. You can add text to the tombstones with a black food safe marker. Put the tombstones and tree in the dip just before serving.