Prepare the steak and asparagus
Put the peppercorns, coriander, fennel, and 1/2 tsp. salt in a spice grinder and grind to a fine powder. Coat the steak with 1/2 Tbs. of the olive oil and then the peppercorn mixture. Set aside for at least 30 minutes and up to 1-1/2 hours.
Toss the asparagus with the remaining 1 Tbs. of olive oil and season with salt and pepper; set aside.
Make the vinaigrette
In a blender, combine all of the ingredients and pulse 2 or 3 times to mix, adding more broth if necessary to achieve a silky consistency.
Grill the steak and asparagus
Prepare a high gas or charcoal grill fire. Grill the steak until nice grill marks form, about 5 minutes. Flip and cook the steak on the second side until an instant-read thermometer inserted in the steak reads 125°F for rare, about 4 minutes. Remove the steak from the grill and put on a cutting board. Tent with foil to keep warm. Let the meat rest while you grill the asparagus.
Spread out the asparagus on the grill and cook, turning a couple of times, until crisp-tender, about 5 minutes.
Assemble the salad
Arrange the asparagus, cress, and mango on 4 plates or a platter. Thinly slice the steak across the grain and arrange over the salad. Drizzle with the vinaigrette and garnish with the red onion and daikon sprouts (if using).