Add apple, garlic, ginger, soy, red pepper, brown sugar, and sesame oil to a food processor. Pulse on high until smooth, adding water a little at a time if needed. Pour into a large sealable bag.

Slice steak very thinly against the grain so it will be fall-apart tender. Add steak to marinade, seal bag, and shake until all the meat is coated.

Let the meat marinate for 30 minutes on the counter or up to 8 hours in the fridge. (Unlike most marinades, we prefer the flavor of the quick 30-minute option!)

Heat 1 T. oil in a large skillet over high heat until shimmering. Arrange half of the meat in a single layer in the skillet and let cook without moving for 1 minute. Toss meat and continue cooking for 3-4 minutes until edges are caramelized, then remove to a plate. Wipe out skillet, heat 1 T. oil, and repeat with the remaining meat.