To make the harissa, combine the red peppers, cayenne, garlic, olive oil, vinegar, and cumin in a blender and puree until smooth. Season with salt and pepper. (Don't limit this sauce to fish alone. It's amazing on grilled steak, pork chops, roasted chicken, or tossed with grilled vegetables.) Lightly oil a grill or stovetop grill pan and heat until medium-hot. Lightly season the flesh side of the fillets with salt and pepper and place them, skin side down, on the hot grill. Cook for 4 to 5 minutes, until the skins are lightly charred and crispy. Turn them over and cook another 2 to 3 minutes. When they're done, the fish should flake with gentle pressure from your fingertip. Serve immediately with a big scoop of harissa.