Salmon Kebabs with Radish Raita

Name: Salmon Kebabs with Radish Raita
Ingredients: 1 cup plain whole-milk yogurt (not Greek); Kosher salt and freshly cracked black pepper; 1/2 cup shredded radish (from about 4 medium radishes), divided; 2 teaspoons vegetable oil, plus more for drizzling; 1/4 teaspoon cumin seed; 1/4 teaspoon black or brown mustard seeds; 1 1/2 pounds skinless salmon fillet, cut into 1-inch pieces (ask your fishmonger to remove the skin); 3/4 teaspoon kashmiri chili powder (or substitute an equal amount of sweet paprika and a pinch or two of cayenne); a small handful of fresh cilantro or mint leaves, for serving