Place bulgur in a large bowl, pour 3 cups boiling water over, cover the bowl with plastic wrap and let sit until tender, about 15 to 20 minutes. Drain well, squeezing out as much water as possible, if needed. Return the cooked bulgur to the bowl and mix in the onion, tomatoes, parsley, mint, and 4 sliced green onions. Place the lime juice, honey, serrano, and 1/2 cup chopped green onion in a blender and blend until smooth. With the motor running, slowly add the oil until emulsified. If the mixture appears too thick, blend in a few tablespoons of cold water, and season with salt and pepper, to taste. Transfer the salad to a platter and drizzle with the green onion vinaigrette.