Begin by thinly slicing the flank steak against the grain. Chop the mixed vegetables into bite-sized pieces and slice the yellow onion. Set aside.
In a small bowl, combine the gochujang, Thai red curry paste, tamari or soy sauce, fish sauce (if using), and pickled ginger juice. Whisk together until smooth and set aside.
Heat sesame oil or olive oil in your wok or skillet over medium-high heat until hot.
Add the thinly sliced yellow onion and sauté for about 2 minutes, until translucent and fragrant.
Add the sliced flank steak and cook for about 3-4 minutes, stirring frequently, until browned and cooked through.
Add the chopped mixed vegetables and stir to combine. Cook for an additional 3-5 minutes, until tender but still crisp.
Pour the prepared sauce over the beef and vegetables. Stir well to coat and cook for another 2 minutes to heat through.
Remove from heat and stir in the fresh basil and sesame seeds. Sprinkle chili flakes on top if desired.
Serve over rice, quinoa, or noodles, and enjoy!
