Cook the pasta as per information given on the packet.
On a frying pan heat 1 tbsp of olive oil. Pan fry button mushrooms from both the sides. Remove from the burner and chop into small pieces.
In a different frying pan heat 2 tbsp of olive oil. Add all purpose flour. Saute it on a low heat till the raw taste of all purpose flour is gone. (around 5 minutes.)
Add milk slowly while whisking it at the same time to avoid lumps.
Add grated cheese, red pepper flakes and salt.
In a different pot heat 1 tbsp of olive oil and saute chopped garlic and green bell pepper and onion on a medium heat for 5 minutes.
Add mushrooms.
Add cooked pasta and mix.
Add Alfredo sauce and mix well. Let it cook for 5 minutes on low heat before serving.