In a blender or small food processor, add the onion, garlic, red pepper flakes, soy sauce, monk fruit, sesame oil, and black pepper. Blend until there are no large chunks of onions or garlic.
In a large freezer bag or container, place your beef, marinade and sesame seeds. Mix the beef in the marinade to completely cover. Marinate at least overnight with 12-24 hours being preferred. Flip your meat at least once during the marinating time.
If you are using boneless short ribs, let the meat rest at room temperature for 20 minutes before cooking. If you are using bone-in, it's not necessary to rest since the beef is thinner.
Place a large non-stick pan on medium-high heat. Once the pan is hot add the beef, being careful to not over crowd the pan. For boneless beef, cook about 5 minutes per side or until it reaches your desired temperature. Bone-in short ribs generally cook a little faster, I cook on both sides until they are a nicely browned on both sides.
Repeat until all of your meat is cooked.
Notes
The marinated beef freezes well. I like to divide the beef into two bags and freeze one for later. You can freeze right after adding the marinade, as the beef defrosts it will continue to marinade.
I find that with a good non-stick pan I don't need to add any extra oil as the beef naturally has a lot of fat. If you are using a different type of pan you may need to add a little oil to prevent sticking.
The nutrition facts below are based on the marinade recipe above with boneless short ribs. This is only an estimation and intended for informational purposes only.