How to Make It
In a small dry skillet, toast the peppercorns and coriander seeds over moderately high heat, shaking the pan frequently, until fragrant, about 1 minute. Transfer the toasted peppercorns and coriander seeds to a work surface and let cool. Using the back of a heavy knife, coarsely crack the peppercorns and coriander. Transfer to a large, sturdy resealable plastic bag. Add the minced garlic and 1/4 cup each of the soy sauce and granulated sugar, then add the steaks and seal the bag, carefully pressing out as much air as possible. Refrigerate for 2 hours.
Meanwhile, in a medium saucepan, heat the oil until shimmering. Add the shallots and cook over moderate heat, stirring frequently, until golden and crisp, about 10 minutes. Using a slotted spoon, transfer the shallots to a paper towel–lined plate. Sprinkle with salt and let cool. Reserve the shallot oil and let cool.
Using a very sharp knife, peel the oranges, carefully removing all of the bitter white pith. Cut in between the section membranes, releasing the orange sections into a bowl.
Light a grill. Remove the steaks from the marinade and scrape off some of the solids. Grill the steaks over a medium-hot fire, turning occasionally, about 10 minutes for medium-rare meat. Transfer the steaks to a cutting board and let rest for 15 minutes.
In a large bowl, combine the fresh orange juice, lime juice, rice vinegar, serrano chile and the remaining 1 1/2 tablespoons of low-sodium soy sauce and 1 tablespoon of sugar. Slowly whisk in 1/2 cup of the reserved shallot oil (reserve the remaining oil for another use) and season the dressing with salt and pepper. Add the orange segments, watercress and frisée. Season the salad with salt and pepper and toss well. Transfer the salad to large plates. Slice the steak across the grain and arrange on the salads. Sprinkle with crispy shallots and serve immediately.