Bake fries according to package directions. In a saucepan, warm oil over medium heat. Add garlic, cumin and chili powder and sauté until mixture is fragrant, about 30 seconds; add beans and their liquid. Simmer until liquid is thickened and reduced by about half, 10 minutes.
Mist an ovenproof serving dish with nonstick cooking spray. Transfer baked fries to prepared dish, mounding them in center, and top with black beans and then shredded cheese. Return to oven and bake until cheese is melted, 5 minutes.
Top smothered fries with dollops of salsa and sour cream and sprinkle with scallions. Pit, peel and slice avocado and place slices at edges of dish. Serve immediately.