Preheat the oven to 400 degrees . Line a baking sheet with parchment. Unfold the puff pastry on a lightly floured surface. Roll out slightly with a rolling pin to smooth out the folds, then cut into 2-by-4-inch rectangles. Place the rectangles on the baking sheet and bake until puffed and golden-brown, 15 to 17 minutes. Transfer the pastries to a rack to cool.
Meanwhile, using a food processor, pulse the red pepper, yogurt and mayonnaise until smooth. Add half of the scallion greens; pulse to chop. Transfer the sauce to a small bowl.
In a large skillet, cook the EVOO and sausage over medium heat, stirring occasionally, until golden, about 5 minutes. Add the green pepper and scallion whites and cook, stirring, for 3 minutes. Pour in the clam juice and marinara and cook until the green pepper is crisp-tender, about 3 minutes. Add the shrimp; stir until firm and pink, about 3 minutes. Stir in the remaining scallion greens.
Split the pastries and place the bottoms on 4 small plates. Divide the shrimp-sausage mixture among the pastry bottoms. Top with the sauce and pastry tops.