1. Combine oil and paprika in a small saucepan, stirring with a whisk. Cook over low heat 2 minutes or until thoroughly heated. Add vinegar, rosemary, if desired, salt, and garlic, stirring with a whisk. Remove from heat.
2. Place pork in a large zip-top plastic bag. Add oil mixture; seal bag. Marinate in refrigerator 8 hours, turning bag occasionally.
3. Prepare grill.
4. While grill heats, remove pork from marinade, discarding marinade. Place pork on a grill rack coated with cooking spray. Grill 20 minutes or until a thermometer registers 155° (slightly pink), turning every 5 minutes. Remove from grill. Let stand 10 minutes before slicing. Cut pork diagonally into 1/2-inch slices.
Serve with: Fragrant Saffron Rice