OPTIONAL: marinade the meat. Toss together 1/4 cup soy sauce, hoisin sauce, and 1 tablespoon minced garlic. Very thinly slice the flank steak against the grain into 1/4th inch thick strips and then into 2 inch pieces. Place the steak pieces in the marinade and set out at room temperature for 20-30 minutes. OR cover tightly and place in the fridge for up to 8 hours. If you want this to be a true 30-minute dinner, skip this step!
While the meat is marinating, prep and cook the veggies. Place 1 tablespoon oil in a large skillet or wok and add in the sliced mushrooms, snap peas, shredded carrots, and chopped red bell pepper. Cook over medium high heat until crisp tender and transfer to a bowl/plate.
Remove the meat and drain off any remaining marinade. Toss the meat to coat with the cornstarch in a large plastic bag. Alternatively use your fingers to work the cornstarch into the meat. Make sure all of the meat is well coated in cornstarch.
Add another tablespoon of oil. Heat until the oil is shimmering and then add in 1/2 the beef so it can be in a single layer. Cook without moving until the beef is well seared, about 1-1/2 minutes. Continue cooking while stirring until the beef is lightly cooked but still pink in spots, about 30 seconds. Transfer to a plate.
Add in the last remaining tablespoon of oil to the pan and heat until shimmering. Add the remaining beef and cook without moving until the beef is well seared, about 1-1/2 minutes. Cook for another 30 seconds. Transfer the rest of the beef to the plate.
In that same skillet or wok, add in the sesame oil, remaining 1/2 cup + 2 tablespoons soy sauce, beef stock or broth, remaining 1 and 1/2 tablespoons minced garlic, minced ginger, brown sugar* (add to your taste preference, we like a lot of sugar in this dish), and red pepper flakes.
Stir and cook (uncovered) over medium heat until sauce thickens a bit and reduces by about a third (about 10-12 minutes). You don't want to reduce it too much so it can still generously coat all the noodles & veggies.
In a small dish, whisk together remaining 1 teaspoon cornstarch with 1 teaspoon water until smooth. Whisk into the sauce.
While the sauce is reducing, boil a small pot of water and cook the ramen noodles for exactly 2 minutes. Drain and rinse in cold water.
Add the cooked veggies, cooked meat, and drained ramen noodles into the sauce. Toss to coat and top with green onions. Add some cracked pepper and additional red pepper flakes if desired. Enjoy immediately.