Using a sharp knife, slice through the outer leaves along one side of the bamboo shoot. Starting on the cut side, peel off the outer leaves. Once the leaves are peeled, you should have a creamy white shoot. Cut about an inch off of the woody fibrous stem until you reach the tender part of the shoot.
Place the shoots in a pot of water. They should be fully submerged. Add rice flour and dried whole red peppers, if using. Bring to a simmer and cook for 15 minutes, until a knife goes through with no resistance. Turn off the heat and let bamboo cool in the water. When completely cooled, slice into strips.Heat oil and garlic in a medium sauté pan. Add mushrooms and cook for 5 minutes over medium-high heat. Add bamboo shoots and continue to sauté for a couple more minutes, until mushrooms are browned and caramelized.