1. In a small bowl, combine chiles, sauce, orange juice, and sugar. Put pork in a baking dish and add marinade, turning pork to coat. Cover and refrigerate at least 2 hours and up to overnight.
2. Preheat oven to 375°. Toast pumpkin seeds on a baking sheet until they have popped and are just starting to brown, 7 to 11 minutes. Let cool. In a food processor, whirl 1/2 cup of seeds into a paste.
3. Heat grill to medium-high. Grill pork, turning once, until an instant-read thermometer inserted into center reads 160°, about 10 minutes per side. Let rest 10 to 15 minutes. Reserve juices.
4. Meanwhile, in a medium pan over medium heat, combine pumpkin seed paste, cream, garlic, chile powder, and salt. Cook, whisking until thickened, 3 to 5 minutes. Stir in reserved pork juices.
5. Slice pork into 1/2-in. medallions. Drizzle with sauce and pumpkin-seed oil and garnish with remaining 1/4 cup toasted pumpkin seeds.
Note: Nutritional analysis is per serving.