In large skillet over medium-high heat, dry-roast chilies, pressing down on all sides until fragrant and toasted, 4 minutes. Do not burn. In bowl, soak in warm water for 20 minutes. Drain, seed and chop coarsely; set aside.
In skillet over medium-high heat, roast tomatillos and red pepper, turning often, until charred all over and softened, about 30 minutes. Let cool slightly; skin and seed.
In blender or food processor, combine chopped chilies, tomatillos, red pepper, onion, garlic, vinegar, oregano, salt and pepper, purée until smooth. Using wooden spoon, press through fine sieve into bowl.
In clean skillet, heat half of the oil over medium heat. Add chili sauce; cook, stirring often, for about 10 minutes or until thickened and slightly darkened. Transfer to bowl; cover to keep warm.
Add remaining oil to skillet; stir-fry shrimp over high heat for 2 to 3 minutes or until bright pink and opaque. Immediately pour sauce over shrimp. Let stand at room temperature for shrimp to absorb flavour, 5 to 10 minutes. Serve slightly warm with toothpicks.