In a large skillet, heat olive oil over medium heat. Add the chopped onion and sauté for about 3 minutes until translucent.
Add the minced garlic and diced red bell pepper to the skillet. Cook for another 2-3 minutes until the pepper softens.
Increase the heat to medium-high and add the ground beef. Cook until browned, breaking it apart with a spatula, about 5-7 minutes. Drain excess fat if necessary.
Stir in the soy sauce, hoisin sauce, sriracha, ground ginger, sesame oil, salt, and pepper. Cook for an additional 2-3 minutes until everything is well combined and heated through.
Remove from heat and stir in chopped green onions and cilantro if using.
To serve, spoon the beef mixture into the lettuce leaves, squeeze lime juice over the top, and enjoy!