Avial ( Tamil: அவியல், pronounced [aʋijal]) is a dish that is common in Kerala as well as Tamil cuisine and Udupi cuisine. It is a thick mixture of vegetables, curd and coconut, seasoned with coconut oil and curry leaves. Avial is considered an essential part of the Sadya, the Keralite vegetarian feast.
Vegetables commonly used in avial are elephant yam, plantain, pumpkin, carrots, beans, Brinjal,cucumber, drum sticks, snake gourd and avarai. Carrots, beans etc. are recent introduction, while the north Keralan Avial includes bitter gourd also. Some people prefer to skip curd or substitute it with raw mango or tamarind pulp. This dish can be made into a gravy or be made into a semi-solid side dish. It is generally eaten with rice. The word "avial" is also used to denote 'boiled' or 'cooked in water' —this sense being derived from the way the dish is made.
It is supposed to have been invented by Bhima (one of the Pandava brothers) during their exile. According to the legend, when Ballav (Bhima's name during this time) assumed his duties as the cook in the kitchen of Virata, he did not know how to cook. One of the first things he did was to chop up many different vegetables, boil them together and top the dish with grated coconut. There are mythological variations. Bheema is said to have prepared Avial, when there were unexpected guests for King Virata and he needed to serve meals for them. There was no sufficient vegetables to cook any single recipe for side dish, so Bheema used what ever available vegetables to make a new dish, which came to know as Avial.
Another narrative version relates to the attempt made by Kauravas to kill Bhima. After poisoning Bhima, Kauravas tied Bhima and threw him to water. Kauravas also communicated that they saw Bhima drowning in water. With the completion of the days of mourning, a funeral feast was planned and preparation were underway. Unexpectedly, Bhima emerged from the water, rescued by the Nagas. With this, preparations for the feast was cancelled. However, Bhima was unhappy with this decision, and decided to mix all of the vegetables to prepare a new dish, that later became popular as Avial.

About Vellai Aviyal:

Aviyal can be prepared yellow in color and white in color(vellai Aviyal),with using ingredients like coconut,yogurt/curd for sourness to maintain white color.So to maintain white color turmeric is avoided which is used in regular aviyal ,you can also skip tamarind by adding curd or mango for sourness.But adding little tamarind won't change that much color if your mango is not sour enough.
Important thing is aviyal is to cut all veggies in same thin matchstick slices uniformly.

Nutritional Info:

For 4 Oz :
Calories
97
Total Fat
4.2g
Sat. Fat
0.9g
Cholest.
0mg
Sodium
208.3mg
Carb.
12.3g
Fiber
1.8g
Sugars
0.2g
Protein
2.7g

Ingredients:

You can use what ever veggies you like,i used below veggies all cut into thin matchstick slices.Don't use tomato.Use vegetables which can hold their shape .

Snake Guard - 1 cup 
Ash Gourd - 1 cup
Yam - 1 cup
Potato - 1 cup
Carrot - 1/2 cup
Drum stick - 1/2 cup
Cucumber - 1 cup
Curry leaf - 3 sprig
Beans - 1/2 cup
Long Bean - 1/4 cup
Butter Beans - 1/4 cup
Small Red Onion (Pearl Onion) - 10 nos
Green Mango - 1
Salt
Tamarind - 1/2 tbsp / Curd - 1/4 cup


For Seasoning:


Coconut Oil - 2 tbsp,More oil the aviyal will taste better and always use coconut oil for aviyal
Mustard Seeds - 1 tbsp
Curry Leaf - 3 sprig
Red chillies - 3

For Grinding:


Coconut Grated - 1 to 1/2 cup(More coconut more tastier)
Jeera/Cumin Seeds - 1 tsp

Grind this to a very coarse mixture.

Method:


1.Take a big Kadai and add all vegetables with little water except mango.Add salt and 1 cup water and cover and let it cook for 20 min,all veggies must be cooked but not overcooked.
2.Then add Tamarind(if using yogurt add at end after switching off stove)and mango.Adding mango now help to maintain its shape.
3.Then add ground mixture and cook for 2 min.Then switch off flame.
If using yogurt add it now.

4.Take another pan and add coconut oil and add mustard seeds and once they splutter add curry leaf and red chillies and add this tadka to the veggie mixture.

Super Tasty and quick Vellai Aviyal is ready,Let ti sit for 30 min to 1 hr for all the taste to blend well.Then Serve it with Hot Rice.