Keep the onions in a bowl of water for 10 min. This will make the peeling easier. Trim-off the top and the root end of the onions with a sharp paring knife. Peel the skins.
Heat a non-stick pan. Add the onions and char them at medium heat, taking care that each onion is turned over atleast once. The charring should not be too much. Remove the onions into a bowl.
Add oil and butter to the same pan. When this becomes hot, add the cumin seeds. When the seeds turn medium-brown, quickly add the garlic paste. Sauté for 1 min and then add all the charred onions.
Sauté for 10 min. Add the cucumber and cook on high heat, until the cucumber loses its moisture.
Add the rest of the ingredients together. Cook for 5 min, sprinkling a little water.