Preheat a grill or broiler for the steaks.While the grill or broiler heats up, combine the lime juice, fish sauce, chile sauce, and sugar in a small bowl. Stir well to dissolve the sugar, then add the minced red chile. Taste and adjust the levels of each ingredient as desired. It should be tart, sweet, and funky.Season the steak generously with salt and pepper and rub with the oil. Grill, turning once, until well-charred but still rosy pink within, 5-8 minutes depending on the thickness. Allow them to rest at least 5 minutes after cooking, then slice against the grain into thin pieces.While the steaks are grilling, combine the watercress, cilantro, mint leaves, cucumber, cucumber, carrot, and tomatoes.When the steaks are done and sliced, add them to the salad and toss everything together with the dressing. Serve immediately while the steak is still hot.