For the salad: Remove the outer leaves of the Brussels spouts and rinse under cold water. Trim the stems and cut in half.
Bring a large pot of lightly salted water to a boil. In a large bowl make an ice bath. Blanch the Brussels sprouts for 2 minutes. Remove from the water and submerge in the ice bath. Drain and place the Brussels sprouts on a towel-lined baking sheet and pat dry.
Heat a large cast-iron grill pan over medium-high heat.
In a large mixing bowl, whisk together the olive oil, garlic, mustard powder, paprika, 2 teaspoons salt and some pepper. Add the Brussels sprouts to the bowl and toss to coat. Reserve the marinade for a later use.
Place the Brussels sprouts cut-side down on the hot grill and cook until slightly charred, 3 to 4 minutes. Flip and cook until the Brussels sprouts are cooked through but still have a semi-firm bite, 3 to 4 minutes. Set aside to cool.
Preheat the oven to 350 degrees F.
Spread the pecans in an even layer on a baking sheet and toast on the center rack of the oven for 8 minutes.
For the dressing: In a medium mixing bowl, add the vinegar, salt, pepper and shallots. Gradually whisk 1/2 cup of the reserved marinade in a steady stream until emulsified.
Place the cooled Brussels sprouts in a serving bowl or on a platter. Add the toasted pecans and pomegranate seeds, and then toss the salad with the dressing. Top with the blue cheese and season with some salt and pepper to serve.