Place 1/2 cup orange juice, 2 tablespoons lemon juice, 1 1/2 teaspoons olive oil, salt, oregano, cumin, and garlic cloves in a blender; process until smooth. Combine orange juice mixture and pork in a large zip-top plastic bag; seal and marinate in refrigerator 2 hours, turning occasionally. Remove pork from bag, reserving marinade.
Heat 1 1/2 teaspoons oil in a large nonstick skillet over medium-high heat. Add pork; cook 4 minutes on each side or until browned. Add reserved marinade; cover, reduce heat to medium-low, and simmer 20 minutes or until thermometer inserted into thickest portion of pork registers 160° (slightly pink). Remove pork from pan; keep warm.
Add 3/4 cup orange juice and 1 tablespoon lemon juice to pan. Bring to a boil; cook until reduced to 1/2 cup (about 5 minutes). Serve sauce with pork. Serve with orange and lemon wedges, if desired. Garnish with oregano sprigs, if desired.