Combine salmon, spinach, panko, 1 Tbps lemon juice, ginger, soy sauce, 1 Tbsp sesame seeds, salt, and pepper in a large bowl. Form mixture into 4 (3 1/2-inch) patties. Place remaining sesame seeds onto a plate, and dip one side of patties into seeds to coat.
Stir together yogurt, dill, garlic, and remaining 1 Tbsp lemon juice in a small bowl.
Preheat a lightly oiled grill pan over medium heat until hot but not smoking. Cook burgers over medium heat, turning, 3-4 minutes per side or until golden brown and cooked through. Grill buns, cut sides down, for about 2 minutes or until golden.
Place burgers on buns, and top with 2 Tbsp yogurt sauce.