Cabbage and red onion offer plenty of prebiotic fodder for the probiotics in Greek yogurt to flourish. (This is the difference between pre- and probiotic foods.) Use the spice rub on tofu or tempeh for a plant-based option that also boosts fiber.
Bring vinegar and 1/2 cup water to a boil in a saucepan. Stir in onion. Remove from heat; let stand 15 minutes. Drain.
Combine cabbage, lime juice, 1 tablespoon oil, and 1/2 teaspoon salt in a large bowl; toss well. Let stand 15 minutes.
Combine chili powder, garlic powder, cumin, paprika, and remaining 1/2 teaspoon salt; rub over chicken. Heat remaining 1 tablespoon oil in a large nonstick skillet over medium-high. Add chicken to pan; cook until well browned and done, about 4 minutes per side. Cool slightly; shred chicken into large pieces.
Heat tortillas according to package directions. Divide chicken and slaw among tortillas; top evenly with onion, avocado slices, yogurt, and pepitas. Garnish with cilantro and radishes, if desired.