Combine both kinds of beans, tomatoes, chilies, corn, scallions, cumin, and oregano in a mixing bowl. Mix thoroughly.
Lightly oil a wide, 2-quart casserole dish and layer as follows: 5 tortillas, overlapping one another; half of the bean mixture; half of the nondairy cheese. Repeat the layers.
Bake the casserole for 15 minutes, or until the cheese is bubbly.
Let stand for a minute or two, then cut into wedges or squares to serve. Pass around salsa and optional vegan sour cream to top each serving.