Shred the zucchini on the large holes of a box grater set in a wide, shallow bowl. Roll up in a kitchen towel, squeeze to remove any liquid, then return the zucchini to the bowl. Stir in the tomatoes, 3 tbsp. EVOO, 2 tbsp. lemon juice, 2 tbsp. parsley and half the garlic; season with salt and pepper. Just before serving, toss with the arugula.
In a large nonstick skillet, heat 2 tbsp. EVOO over medium-high heat. Season the cod with salt and pepper and add to the pan; cook, turning once, until browned on both sides, about 8 minutes.
Meanwhile, make the toasts: Preheat a grill pan or broiler. Brush the bread slices lightly with EVOO and cook until crisp on both sides, about 3 minutes.
In a small bowl, combine the remaining 1/4 cup parsley, the remaining garlic and the lemon zest; season with salt and pepper. Sprinkle over the fish. Serve the fish with the salad and toasts.