Prep ingredients: Preheat broiler with top rack 6 inches from heat source. Peel and finely chop 1 teaspoon garlic. Trim scallions, then thinly slice. Scrub radishes, then thinly slice into half-moons. Transfer pulled pork to a medium bowl, then use your fingers or two forks to break it into large pieces.
Pickle radishes: In a small bowl, combine 2 teaspoons vinegar, ⅛ teaspoon sugar, and a pinch of salt, whisking until sugar dissolves. Add radishes to bowl and toss to coat. Let stand, stirring occasionally, until ready to serve.
Make slaw: In a large bowl, stir to combine mayonnaise, scallions, half of the chopped garlic, 1½ teaspoons vinegar, 1 tablespoon oil, and a pinch of sugar. Add 4 cups shredded cabbage and toss to combine. Season to taste with salt and pepper.
Char tortillas: Toast tortillas over a gas flame until lightly charred in spots, 5–10 seconds per side. (Alternatively, broil on top oven rack until lightly charred, about 10 seconds. Watch closely as broilers vary). Wrap tortillas in foil as you go to keep warm.
Season pork: Heat 1 tablespoon oil in a medium ovenproof skillet over medium. Add remaining chopped garlic and 1 tablespoon of the taco seasoning, and cook, stirring, until fragrant, about 30 seconds. Stir in ¼ cup water and bring to a boil. Remove from heat, then stir in pork.
Broil pork & serve: Lightly drizzle pork with oil. Broil on top oven rack until pork is crispy and browned in spots, about 6 minutes (watch closely). Build your own tacos at the table with pulled pork, warm tortillas, cabbage-scallion slaw, pickled radishes, and guacamole.