Rehydrate the 5 shiitake mushrooms in hot water for 1-2 hours. Slice thinly and set aside. Rinse the white button mushrooms in water and then roughly slice to 1/4 inch thickness.
Peel the jumbo carrot, and cut into thin matchsticks, set aside. Peel the medium onion and cut in half. Slice the onion lengthwise, set aside. Finely mince 12 garlic cloves and set aside.
Chop the green onion in diagonal 1 inch long pieces. For the white parts of the green onion, cut them in half lengthwise, otherwise the taste may be a bit too pungent.
Rinse the spinach in cold water, spinach bunches can have a lot of dirt hiding inside so rinse well. Bring a small pot of water to boil and add a generous pinch of salt to the pot. Place the spinach, stem side down first, in the boiling water. Cook for 30-40 seconds, and then rinse spinach in cold water to preserve its vibrant green colour. Press the spinach to remove any excess water.
Cut the spinach using a pair of scissors. Season the spinach with 1 tbsp of sesame oil and 1 tablespoon of soy sauce. Mix and set aside.
If using, slice the red bell pepper into long strips.
For the 1lb of beef (or other meat), slice against the grain into thin strips (1 inch long, 1/4 inch wide). Season with 1 tbsp of cornstarch, 1 tbsp of minced garlic, cracked black pepper, 1/2 tbsp of sesame oil and 1 tbsp of soy sauce. Mix the shiitake mushroom slices into the mixture as well.