In a blender, purée chopped jalapeño with fresh lime juice, plain yogurt, fresh cilantro, and ground cumin until very smooth.
Heat canola oil in a large cast-iron skillet on medium-high. Add lean white ground turkey and cook, breaking it up with a spoon until golden brown and crispy, 6 to 8 minutes.
Add garlic, jalapeño, and freshly grated ginger and cook, tossing, for 1 minute.
Remove from heat and add low-sodium soy sauce, lime juice, and up to ¼ cup water (if it seems dry).
Sprinkle with scallions. Spoon into butter lettuce leaves and serve with cilantro sauce and sliced radishes, if desired.
