Marinate the steak with 1 tbsp of soy sauce and black pepper, set it aside for 15 minutes or longer.
Heat a gas or charcoal grill, grilling pan or in my case, a cast iron grill over high heat until very hot. Lower to medium-low heat and grill to desired doneness, 5-6 minutes per side for medium-rare. Transfer to a bowl and let rest for at least 10 minutes.
Meanwhile, let's make the sauce. Cut the lemongrass stalk into thin slices. Pile the sliced lemongrass together to chop into smaller pieces. Transfer it into a small bowl. Add the rest of the sauce ingredients: salted crab juice, palm sugar, fish sauce, lime, chopped garlic, bird eye chilies and mix it well.
Place the papaya into a mortar, add half of the sauce to the papaya and pound a few times just to soften the papaya. Use a spatula to turn the papaya and sauce mixture a few time in between the pounding in order to really mix the sauce in well. Scrap the papaya and sauce from the mortar and place it into a large mixing bowl. Set it aside for now.
Trim away any excess fat from the steak and thinly slice across the grain. Pour the accumulated juices from the steak and the sliced steak into the papaya mixture. Add the remaining half of the sauce, red bell peppers, yellow bell peppers and shallot. Toss to combine. Taste it and add more salt, sugar or bird eye chilies to match your preference. Serve with rice, fresh basil and cilantro.