Cook ground pork and yellow onion in a skillet over medium-high heat for 8 to 10 minutes, breaking up the meat and cooking it to 160°F. Spoon off excess fat.
Stir in garlic, tomato paste, ancho powder, cumin, oregano, orange zest, salt and pepper and cook for 1 minute.
Add 1/2 cup water and simmer for 5 to 7 minutes until the meat is moist but no loose puddle remains.
Freeze after cooking: divide filling into 4 shallow containers, refrigerate within 2 hours and chill fully. Seal, label and freeze for up to 2 months; keep tortillas, serving onion and lime separate.
Thaw filling overnight in the refrigerator. Reheat in a covered skillet over medium-low heat for 6 to 10 minutes with a little reserved water, stirring until the meat reaches 165°F.
Warm tortillas in a dry skillet for 20 to 30 seconds per side. Divide filling among 8 tortillas and top with measured white onion.
Serve 2 tacos per portion with lime wedges for squeezing.