Delicious Thai beef salad recipe

Ingredients: For the Beef: 1 pound beef sirloin or flank steak 1 tablespoon vegetable oil Salt and freshly ground black pepper, to taste For the Salad: 4 cups mixed greens (such as lettuce, arugula, and cilantro) 1 cup cherry tomatoes, halved 1 cucumber, thinly sliced 1 red onion, thinly sliced 1/2 cup fresh mint leaves