Salt mackerel fillets generously and let sit for 20 minutes
This draws out moisture and helps with grilling
Rinse salt off and pat dry
Mix soy sauce, vinegar, lemon juice, mirin, and sugar for ponzu
Preheat grill or broiler to high
Grill mackerel skin-side down for 4-5 minutes
Flip and grill another 3-4 minutes
Serve with ponzu sauce, grated daikon, and lemon wedges