Preheat the oven to 450 degrees. Cook the bacon in a large skillet over medium heat, stirring from time to time, until browned and crispy. Transfer to paper towels to drain; keep warm. Add the onion slices to the drippings in the skillet; sprinkle with the sugar and season with salt and pepper. Cook until light brown and tender, 5 to 7 minutes. Taste for seasoning.
Combine the scallions, capers and parsley in a food processor. Add salt and pepper to taste and half of the lemon zest; pulse gently to chop and blend. Turn the processor on and add the olive oil through the top in a steady stream. Transfer the scallion pesto to a bowl; set aside.
In a small bowl, whisk the creme fraiche and the remaining lemon zest until smooth. Season with salt and pepper; set aside.
Roll the pizza dough into an 8-by-14-inch rectangle on a lightly floured surface. Roll the dough around the rolling pin and unroll it onto a baking sheet lined with parchment paper. Place in the center of the oven and bake for 10 to 12 minutes, or until golden brown.
Spread the creme fraeche mixture on the crust. Dot with the onions and some of the bacon drippings from the pan; sprinkle with the bacon. Slice into pieces and drizzle with scallion pesto.