Heat a large roasting pan in 220C oven (fan-forced) for 15 minutes.
Meanwhile, scrub potatoes clean under cold water. Cut into 2cm thick wedges. Pat dry with paper towel. Combine chilli powder, oregano, garlic and oil in a large bowl. Add wedges. Toss well with clean hands to coat in spice mixture.
Carefully, remove hot pan from oven. Arrange wedges in a single layer over base. Bake in 220C oven (fan-forced) for 25 minutes, or until tender. Remove from oven. Scatter beans, corn and chicken over wedges. Spoon canned tomatoes over top. Sprinkle with cheese.
Return to same oven. Bake for 12-15 minutes, until cheese is melted and lightly browned.
Mash avocado with lime juice on a plate. Stir in onion.
Dollop avocado and salsa over hot wedges to serve.

Shredded, skinless, cooked chicken breast is available from the deli counter in supermarkets.
Alternatively, substitute leftover skinless, roast chicken.
Replace frozen corn kernels with frozen mixed vegetables, if preferred.