In a small bowl, combine flour, salt, lemon zest, garlic, and sumac, then whisk to combine.
Pat salmon dry on both sides, then place on a plate or tray. Pour dry ingredients on top, pressing gently onto the salmon, then cover with plastic wrap and refrigerate for 2 hours.
Meanwhile, make the marinade. Combine olive oil, vinegar, shallots, and serrano in a medium bowl. Whisk, then set aside.
When ready, preheat a large skillet over high heat. Add 2 Tbsp olive oil. Shake any excess flour off of fish, then sear flesh side down for 4 minutes, undisturbed. Carefully flip the fish using a fish spatula, then sear skin side down for an additional 3 minutes. Transfer salmon to a bowl or dish with deep sides, then immediately pour the marinade on top. If eating that day, leave fish on counter to cure for at least 2 hours. If serving the next day, cover fish and place in refrigerator overnight. Salmon is best when served at room temperature, so make sure to bring it out 1-2 hours before serving.
To serve, pour sliced olives and sun dried tomatoes on top, then garnish with fresh dill. Can be eaten as is or smushed on top of sliced, toasted bread.