For the Salmon: Heat the oil in a skillet (cast iron is good) over medium-high heat. In a bowl, stir together the flour, chili powder, paprika, brown sugar, onion powder, garlic powder, cumin, cayenne, salt and pepper. Coat the flesh of the salmon liberally with the blackening spice.
Place salmon in hot skillet. Cook 3-4 minutes per side or until coating is blackened and forms a nice crust and salmon is cooked through (medium-well, just slightly pink in the center). Allow salmon to rest for 5 minutes, then flake with a fork.
For the Salsa: In a bowl, gently stir together the avocado, corn, tomato, red onion, cilantro, lime, salt and pepper. Refrigerate until ready to serve. Note: Can be made up to an hour in advance.
For the Dressing: Add yogurt, mayo, buttermilk, lime, garlic, green onions, cilantro, salt and pepper to a food processor. Process until smooth. Add more buttermilk as needed until desired consistency is reached (you'll want it to be thin enough to drizzle, but not so thin that it slides off the tacos). Refrigerate until ready to serve. Note: Can be made up to several hours in advance.
To Assemble Tacos: On a warmed corn tortilla place flaked salmon followed by Avocado Corn Salsa and some shredded cabbage. Drizzle with Cilantro Ranch Dressing. Serve with lime wedges.