In a small bowl, toss the cucumber slices with the rice vinegar, ¼ teaspoon of the sesame oil, and a pinch of salt. Set aside.

Bring a small pot of water to a boil. Drop in the bean sprouts and cook for 1 minute. Drain and set aside.

Heat another ½ teaspoon of the sesame oil in a medium skillet over medium heat. Add the carrots and a pinch of salt. Cook, stirring, for 1 to 2 minutes, or until a little bit soft, and then remove from the pan and set aside.

Heat the remaining ½ teaspoon sesame oil in the skillet and add the spinach and tamari. Cook, tossing, for 30 seconds, or until just wilted. Remove from the skillet and gently squeeze out any excess water from the spinach.

Assemble the bowls with the rice, cucumber slices, bean sprouts, carrots, and spinach. Top with a fried egg or baked tofu. Add the mushrooms, if using. Sprinkle with sesame seeds and drizzle generously with the gochujang sauce. Serve with kimchi and scallions, if desired, and the remaining gochujang sauce on the side.