Whisk together the olive oil, 4 cloves of garlic, ginger, fish sauce, soy sauce, and sesame oil in a bowl, and pour into a resealable plastic bag.
Add the beef sirloin tip, coat with the marinade, squeeze out excess air, and seal the bag. Marinate in the refrigerator for 2 hours.
Remove the beef sirloin tip from the marinade, and shake off excess. Discard the remaining marinade.
Heat vegetable oil in a large skillet over medium-high heat and stir in the beef. Cook and stir until the beef is evenly browned, and no longer pink.
Place beef on a plate and set aside. Reduce heat to medium, adding more vegetable oil to the skillet if needed. Stir in 2 cloves of garlic, green onion, and onion; cook and stir until the onion has softened and turned translucent, about 5 minutes. Stir in green beans, beef broth, lime juice, basil, mint, red pepper flakes and pepper. Return beef sirloin to skillet and toss to combine.