In a small bowl, add the cucumber slices and toss with 1 tsp rice vinegar, ½ tbsp sesame oil, and season with a pinch of sea salt. Set aside.
Heat 1 tbsp sesame oil in a medium skillet over medium-high heat. Add the sliced shiitake mushrooms and cook for 3–4 minutes until cooked and browned. Season with soy sauce. Remove from the pan and set aside.