For the steak and peaches: Put the pineapple juice, brown sugar, soy sauce, mirin, sesame oil, garlic, scallions, onion and 1/4 teaspoon pepper in a blender and blend until smooth. Combine three-quarters of the marinade with the flank steak in a large resealable plastic freezer bag. Combine the remaining marinade with the peaches in a separate resealable plastic freezer bag. Refrigerate both at least 45 minutes and up to 4 hours.
Prepare a grill for high heat.
For the salad: Using the tongs from a Food Network 17-piece Grilling Tool Set, grill the romaine cut-side down until lightly charred, about 1 minute. Transfer to a large platter. Put a stainless-steel mesh Food Network Grilling Tray on the grill. Add the onions and grill, tossing occasionally, until tender and charred in spots, about 5 minutes.
Remove the steak from the marinade, shake off any excess, and put on a baking sheet. Sprinkle both sides with salt and pepper. Remove the peaches from the marinade to a plate. Grill the steak until well browned, about 5 minutes per side for medium rare. Set aside on a cutting board to rest. Brush the peaches with olive oil and grill cut-side down just until grill-marks appear, about 1 minute.
For the dressing: Meanwhile, whisk together the lime juice, olive oil, pineapple juice and 1/2 teaspoon salt in a small bowl until combined.
Thinly slice the steak against the grain. Cut the peaches into thick wedges.
Scatter the cucumbers, tomatoes, onions, peaches, cilantro and basil over the romaine. Top with the steak and sprinkle with the sesame seeds. Drizzle with the dressing.
Copyright 2020 Television Food Network, G.P. All rights reserved.