Put a large piece of aluminum-foil near cooktop. Heat a dry, heavy skillet over medium-heat till hot.
Add corn tortilla, then cook for 30minutes on each side or till softened & lightly charred. Move to aluminum-foil & fold round tortilla to remain warm. Repeat with remaining tortillas.
Then in a medium-bowl coat peeled & deveined shrimp in cornstarch.
Heat oil in a large-skillet till almost smoking. Shake any excess cornstarch out of shrimp and carefully add in a few at a time to wok, providing every shrimp some space to crisp-up. Cook, turning frequently with a spatula till shrimp are pink for 2-3minutes.
Add fresh garlic, pepper and salt, toss with spatula till spices have been spread and garlic is fragrant for a few minute. Remove from heat and transfer shrimp to a plate.
Assemble tacos: top one warm-corn tortilla with 3-4 shrimp & sprinkle with chopped cabbage, cilantro and radishes, if desirable.
Drizzle with desired amount of shrimp taco-sauce. Repeat with remaining tortillas. Serve with chopped jalapeño and lime wedges if desired.