Slice steak thinly to about ⅛-¼ inch thick strips. The thinner it is, the quicker it will cook and sear.
In a medium mixing bowl, whisk the brown sugar, soy sauce, cornstarch, and lemon juice until smooth.
Add the marinade and steak to a gallon zipper bag. Let marinade for a minimum of 30 minutes.
Steam or Blanch the broccoli for about 3 minutes, until it turns bright green and is softening but still has a bite.
Sautee the broccoli in a couple tablespoons of canola oil for about 3-4 minutes. Just enough time to slightly brown the broccoli, stirring frequently. Set aside.
In a medium mixing bowl, whisk the sauce ingredients until smooth.
Add 2 more tbsp of canola oil to the same skillet used to sautee the broccoli on medium-high. Sautee the beef in several batches, allowing for a single layer. Transfer each batch to a plate and set aside.
Reduce the heat to medium and cook the sauce for 3-5 minutes until it thickens.
Transfer the beef and broccoli to the pan and cook for 3 minutes, until everything is coated in the sauce and everything has heated through.
Top with sesame seeds and siracha, serve immediately.
Serve over Ramen or rice.