Preheat oven to 375 degrees F. Line a baking sheet with parchment paper; set aside.
Unroll puff pastry dough and cut into 8 equal rectangles. Transfer the rectangles to the prepared baking sheet. Beat the egg yolk with 2 teaspoons water. Use a pastry brush and brush the edges of the rectangles with the egg wash. Fill the center with 1-2 tablespoons shredded cheese, then top with a slice of bacon on the diagonal. Top the bacon with another tablespoon of cheese, then a slice of tomato. Season with salt and pepper.
Fold in 2 corners of the rectangles towards the center. The corners should not touch, but should cover a bit of the tomato. Brush the folded corners with egg wash then transfer the baking sheet to the refrigerator to chill for 15 minutes.
Bake the puffs until golden and cheese is melted, about 15-20 minutes. To serve, top with shredded lettuce, chopped tomato, chopped bacon and a drizzle of ranch dressing.