Prepare the shrimp according to package directions. Season the tomato with salt, to taste, and set aside.
Place chips in a 9x13-inch baking dish. Sprinkle half the cheese over the chips. Drizzle with barbecue sauce. Scatter shrimp and jalapenos over chips, then sprinkle remaining cheese on top and bake until cheese melts and nachos are golden on top, about 10 minutes.
Scatter the tomatoes and scallions over the nachos and serve immediately with additional sauce and sour cream.