In a large mixing bowl, combine the ground beef, breadcrumbs, chopped onions, minced garlic, chopped cilantro, lime zest, lime juice, ground cumin, salt, black pepper, and red pepper flakes (if using).

Add the beaten egg to the mixture and combine thoroughly until all ingredients are well incorporated. The mixture should be moist but firm enough to form meatballs.

Preheat a large skillet over medium heat and add the olive oil.

While the skillet heats up, shape the meat mixture into small meatballs, about 1 inch in diameter.

Once the oil is hot, carefully place the meatballs in the skillet, making sure not to overcrowd the pan. You may need to cook them in batches.

Cook the meatballs for about 8-10 minutes, turning them occasionally to ensure they are browned on all sides and cooked through. The internal temperature should reach 160°F (70°C) for beef or 165°F (74°C) for turkey.

Once cooked, remove the meatballs from the skillet and place them on a paper towel-lined plate to absorb any excess oil.

Serve the lime meatballs warm, garnished with additional chopped cilantro and lime wedges if desired. They pair well with rice, in tacos, or on their own as an appetizer.