Season cod pieces evenly with olive oil, spice blend and zest, then set aside. Heat a large thick-bottomed skillet on medium heat. Add butter pieces. When butter turns light brown, add the garlic slices. Fry garlic until golden brown, then remove from skillet. Do not overcook. Add cod to skillet. Fry 2-4 minutes, then carefully flip and continue to fry for 2-4 minutes until cod is cooked through. Baste fish with butter during cooking. Transfer cod to 4 plates. Pour butter over cod. Top with garlic slices and salsa.