In a large pot of boiling salted water, cook pasta according to packaging. Drain, set aside and reserve 1 cup of pasta water.

In a large pan, heat oil over low heat add garlic and cook stirring until softens about 1 minute. Add mushroom, red pepper flakes, salt and pepper to taste. Stir to mix, and when mushroom starts to cook, add lemon juice if using and continue to cook until the liquid starts to evaporate and the mushroom starts to turn brown. Add parsley and spaghetti and stir and mix all ingredients together. If pasta needs moisture gradually add some of the reserved water. Cook for about 2 – 3 minutes, remove from heat and serve promptly.