Stir together the yogurt, lemon juice, olive oil, garlic, coriander, cumin, 1/4 TSP salt, and pepper to taste in a small bowl. Pour half of the sauce into a large resealable plastic bag; cover and refrigerate the remaining sauce.
Add the salmon to the bag and turn to coat with the marinade. Refrigerate for 20 to 30 mins, turning the bag over once.
Preheat a grill to medium-high. Remove the salmon from the marinade and blot off excess yogurt with paper towels.
Lightly oil the grill and add the salmon; cook, turning once, until browned on the outside and opaque in the centre, 5 to 6 mins per side, depending on the thickness.