In a large bowl combine vegetable oil, minced garlic, sliced onion, lemon juice, Worcestershire sauce, beef bouillon granules, dried thyme, dried oregano, crushed red pepper flakes (if using), and salt and pepper to taste.
Add the sliced steak to the bowl and toss to coat in the marinade. Cover and let marinate at room temperature for 30 minutes.
Heat a large skillet over high heat until very hot. Add a little oil if the skillet is dry. Sear the steak strips in batches without overcrowding, 1–2 minutes per side, until browned; transfer seared strips to a plate and reserve pan juices.
Reduce heat to medium and add the unsalted butter to the same skillet. Add the broccoli florets and stir-fry, tossing occasionally, until the broccoli is tender-crisp and the pan sauce reduces to your liking, about 4–6 minutes.
Return the seared steak to the skillet with the broccoli and toss briefly to reheat and coat with the sauce, about 1–2 minutes.
Serve the steak and broccoli over cooked white rice.