Preheat the oven to 400 degrees . In a skillet, cook the bacon over medium heat until crisp, 7 to 10 minutes; drain on paper towels. Reserve the bacon grease in a small, heatproof bowl and reserve the skillet. In a large bowl, combine the pear, 1/2 cup cheese, the tarragon and 1/2 tablespoon of the reserved bacon grease; season with salt and pepper.
Using a rolling pin, roll out the puff pastry to a 12-inch square; cut the pastry into quarters. Arrange in a single layer on a baking sheet. Divide the pear mixture evenly among the squares, reserving the bowl. Moisten the edges of the pastry with water, then fold over to enclose the filling, pressing the edges to seal. Brush each turnover with the cream, cut a few slits on top and sprinkle with the remaining 1/4 cup cheese. Bake until browned, about 20 minutes.
In the reserved large bowl, combine the spinach, red onion and cooked bacon. Reheat 1 tablespoon of the reserved bacon grease in the reserved skillet, then remove the pan from the heat and swirl in the lemon juice. Drizzle over the salad, season with salt and pepper and toss. Serve with the turnovers.