For the Quick Pickled Onions, place onions in medium heatproof bowl. Bring remaining ingredients to simmer in small saucepan on medium-high heat. Remove from heat. Pour over onions in bowl. Cover. Let stand 30 minutes.
Meanwhile, for the Tacos, mix mayo, sour cream, lime juice, 1 tablespoon of the crushed jalapeno pepper, sugar and ¼ teaspoon of the salt in medium bowl. Add coleslaw mix, tossing to coat well. Cover. Refrigerate until ready to serve.
Mix corn meal, remaining 1 tablespoon of crushed jalapeno pepper, chili powder, remaining ¾ teaspoon salt, and garlic powder in shallow dish. Coat fish evenly with corn meal mixture.
Heat oil in large nonstick skillet on medium heat. Add fish; cook 3 to 5 minutes per side or until golden brown and fish flakes easily with a fork. Cut fish into 8 portions. Serve in warmed tortillas topped with slaw and pickled red onions.
