Make pico de gallo by combining the first 7 ingredients in a bowl. Cover and refrigerate until needed (can be made a few hours before needed).
Preheat the oven to 400 degrees F. Place the halibut skin-side-down in a single layer in a parchment paper-lined baking dish. Combine the chili powder, 1 tsp. cumin and olive oil in a small bowl. Brush the mixture on the fish. Season the fish with salt. Bake the halibut 15 minutes, or until cooked through. Plate the fish, top each fillet with some pico de gallo, garnish with lime slices and enjoy.