Step 1Toast the bulgur in a skillet over medium-high heat until it smells nutty, about 5 minutes. Remove from the heat, add the water and let stand for 1 hour to soften, stirring occasionally. (The dish can be prepared to this point a day ahead and refrigerated tightly covered; bring to cool room temperature before serving.)
Step 2Cut the zucchini in quarters lengthwise and then in half-inch cross-wise pieces. Place them in a strainer or colander and sprinkle generously with salt. Toss to distribute the salt and set aside for 30 minutes, placing the strainer over a bowl to collect the water that is drawn out.
Step 3Fluff the bulgur with a fork and place it in a large mixing bowl along with the red onion. Rinse the zucchini well, pat dry with a kitchen towel and add it to the red onion and the bulgur. (The dish can be prepared to this point up to 4 hours in advance and refrigerated tightly covered.)
Step 4When ready to serve, stir in the lemon juice and olive oil and season to taste with salt, more lemon juice or olive oil, and black pepper as needed. Fold in the arugula leaves and transfer the mixture to a serving bowl. Sprinkle the toasted pine nuts over top and serve. This makes about 6 cups salad.