Whisk together mayonnaise, salt, mustard, onions, peppers, paprik, and hot sauce; set aside for 30 minutes for flavors to meld. Taste and adjust seasoning. Combine with shrimp in a non-reactive bowl and refrigerate for 4 to 6 hours. To serve, slice the top off the tomatoes and hollow them out; fill with marinated shrimp salad, serve on a bed of lettuce, and garnish with parsley.