Preheat the oven to 375 degrees F. Place the pecans on a baking sheet in one layer and bake until golden, 6 to 8 minutes. Let cool, then coarsely chop; set aside.
Shred the Brussels sprouts using the large holes of a box grater or a mandoline. Coarsely chop any ungrated pieces with a knife.
Combine the mayonnaise, mustard, honey, vegetable oil and orange zest in a large bowl and whisk to combine. Whisk in the vinegar and orange juice until smooth. Add the shaved Brussels sprouts and toss to combine. Season with salt and pepper. Transfer to a serving dish and scatter the pecans and pomegranate seeds on top. Refrigerate 2 to 4 hours before serving.