Season the shrimp with salt and pepper, to taste. In a small skillet over medium heat, heat 2 tablespoons of the olive oil and saute the shrimp for 1 1/2 minutes on each side. Reserve for garnish.
Place 2 tortillas on an ungreased baking sheet, sprinkle half the cheeses and 1 1/2 tablespoons pesto on each, and season, to taste, with salt and pepper. Stack the 2 layers and cover with the remaining tortilla. Brush with 1 tablespoon oil and sprinkle evenly with ancho chile powder. May be prepared 1 day ahead up to this point and refrigerated. Bake for 8 to 12 minutes or until the tortillas are slightly crisp and the cheese has melted.
Cut into quarters and serve hot, garnished with the shrimp, more pesto, and sour cream.
In a food processor, combine cilantro, garlic, pumpkinseeds, lime juice, salt and pepper. With the motor running, slowly add the olive oil until sauce is emulsified. May be prepared up to 2 days ahead, covered, and refrigerated. Bring to room temperature 1 hour before serving.