Tampico Pumpkin-Seed Green Sauce

I first ate and loved this sauce at the Restaurante Diligencia in Tampico, Tamaulipas. They serve it with pan-fried fish fillets and fried fish roe, accompanied by steaming hot tortillas. I have found it marvelous with grilled fish, chicken and duck breasts, fried shrimp, and roast lamb. It is great in the fillings for Sopes. The sauce should be very buttery and make your mouth tingle!