Puree cilantro, arugula, mint, crushed red pepper flakes, garlic, kosher salt, ground black pepper, lime juice, and olive oil in a blender until smooth. Store in the refrigerator with some olive oil poured over the top. It will keep for up to one week in the refrigerator or in the freezer for up to two months.*

Heat the grill to high, approximately 450° F.

Brush the fish on both sides with oil and season with salt and pepper. Grill the salmon, meat side down, until lightly golden, about 4-5 minutes. Turn the fillets over, reduce the heat to medium or move to a cooler part of the grill, and cook until the skin is browned and the meat is just cooked through but not falling apart, 2-3 minutes more.

Transfer the fish to serving plates or a platter and spoon a few tablespoons of chimichurri over each fillet. Serve immediately.