Place cucumber slices in a bowl and add the 1/2 teaspoon salt. Let it sit for 10 minutes.
In a small bowl, combine beef with Korean soy sauce for soup, soy sauce, sesame oil, garlic, sugar, and pepper. Set aside.
Squeeze out the cucumbers to remove the moisture.
Heat oil in a skillet over high heat. Add the cucumber slices and stir-fry for 1-2 minutes. Remove the cucumbers and set aside.
Add the beef and red chili slices to the skillet and stir-fry until they are just browned. Return the cucumbers and toss with beef and chili. Sprinkle sesame seeds and serve with rice.