How to Make It
Preheat broiler to high with oven rack 6 inches from heat. Broil chiles 8 minutes or until blackened, turning frequently. Place in a bowl; cover with plastic wrap. Let stand 15 minutes. Peel, seed, and slice chiles into 1/4-inch-wide strips.
Heat oil in a skillet over medium-high. Add onion; sauté 5 minutes. Add sliced chiles and garlic; sauté 2 minutes. Stir in crema and salt; cook 1 minute. Divide chile mixture among tortillas; top with radishes, corn, and chayote, if using.