In a large skillet, cook the bacon over moderately high heat until browned and crisp, about 8 minutes. Drain the bacon on paper towels.
In a bowl, mix the mayonnaise with the sour cream and mustard and season with salt and pepper. Add the bacon, smoked trout, cherry tomatoes, frisée and scallions and toss to coat. Spoon the salad into the pita breads and serve.