In a bowl, combine marinade ingredients. (Leave out the steak.)
Set aside 1/3 cup marinade and then add steak to the marinade and toss until evenly coated. Let marinate for 30 minutes up to an hour.
Drain marinated beef. In a large bowl, toss together cornstarch, Bayou City Seasonings, cumin, and beef. In a skillet on medium-high heat, heat 2 tablespoons of grapeseed oil. Add steak a little at a time to not overcrowd the pan and cook until seared, 1 to 2 minutes per side. Remove steak and set aside.
Return the skillet to medium heat. Add remaining 1 tablespoon grapeseed oil, then add chili flakes, 1 tablespoon sesame seeds, garlic, green onion, and a pinch of salt. Stir and cook for about 2 minutes. Add in broccoli and cook, about 4 minutes. Add in broth and let cook until broccoli is tender, 3 or 4 minutes.
Add hoisin and 1/3 cup marinade that we set aside. Bring to a simmer. Add back cooked steak and toss until evenly coated. Let cook, stirring, until the sauce thickens.
Garnish with more sesame seeds and green onions. Serve with rice!