Preheat a cast iron-skillet over medium-low for 3 minutes.
Add rice (if using) and toast until deeply golden, about 10 minutes; transfer to a bowl to cool.
Add peanuts to skillet and toast until fragrant and golden, about 5 minutes. Transfer to a second bowl and let cool.
Grind rice into a fine powder in a spice grinder. Transfer to a bowl.
Pulse nuts in spice grinder until roughly chopped.
Halve cucumber lengthwise, placed halves, cut side down on cutting board, and smash with back of hand until cracked and lightly smashed. Cut smashed cucumbers into chunks.
Toss cucumber chunks with ½ teaspoon salt in a colander set over a bow; set aside until ready to serve.
Add sliced shallots to a small bowl; cover with cold water and set aside.
Preheat cast-iron skillet over medium-high heat for 5 minutes.
Season steak with 1 teaspoon salt and ½ teaspoon pepper.
Place steak in skillet and cook until charred and beads of moisture begin to form around edges of steak, about 3 minutes. Flip and continue cooking until an instant-read thermometer inserted in the center registers 125ºF for medium-rare, about 3 more minutes. For medium cook to an internal temperature is 135ºF, about 4 minutes per side.
Transfer steak to a clean plate, tent loosely with foil or parchment paper and let rest 10 minutes.
Meanwhile, whisk together lime juice, fish sauce, honey, and chili in a medium bowl.
Thinly slice steak (¼ inch thick) across the grain, add to bowl with dressing and toss to coat.
When ready to serve, toss bibb lettuce and herbs together on a large platter. Top with salted and drained cucumbers. Drain shallots then add to platter.
Arrange steak slices over top then drizzle dressing over salad.
Sprinkle with toasted rice powder and peanuts; serve.