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Preheat the oven to 375 degrees F (190 degrees C) and line a sheet pan or cookie sheet with parchment paper. Unroll pie dough on the prepared pan.
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Heat vegetables in a microwave-safe bowl, with no added water, until warm, about 3 minutes. Line a platter with paper towels, and pour vegetables on the paper towels to drain thoroughly.
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Slice bacon crosswise into 1/4-inch strips, or lardons. Place lardons in a nonstick skillet and cook over medium heat until brown and crispy, 3 to 5 minutes. Line a plate with paper towels; remove lardons to the plate to drain; set aside. Leave bacon fat in the skillet.
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Add onion to the same skillet, and cook until softened, 3 to 5 minutes. Sprinkle flour over all, and stir 1 to 2 minutes, making sure all the flour is moistened by the bacon fat. Gradually stir in cream, stirring constantly, until bubbly, 3 to 5 minutes.
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Crumble Boursin into sauce and stir until melted, 1 to 2 minutes. Remove from heat and allow to cool, 3 to 5 minutes; sauce will be thick. Season with salt and pepper.
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Stir drained vegetables into sauce until well mixed; pour onto pie crust and spread to within 2 inches of crust edges. Fold up the edge over the vegetables; dampen fingers to pinch dough into little pleats. Brush dough with egg wash.
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Bake in the center of the preheated oven, until crust is golden brown, 35 to 40 minutes.
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Remove from the oven; scatter lardons over the top. Cool on a wire rack for about 5 minutes. Cut into 6 pieces, and serve warm.
