As the name suggests, karela are bitter but are known to have therapeutic value, especially for those suffering from diabetes. When tomatoes and other vegetables are mixed with it, the bitterness is reduced. Traditionally people first scrape karela and remove the hard skin. Then they rub salt in them and let them rest for about 1 hour. Then they squeeze out bitter water before using. Karela can be used with any meal or in a sandwich or pita bread. You may prepare them in advance, and refrigerate or freeze them. Or you may freeze uncooked karela. Buy them fresh, when in season, and rinse, trim, and cut them before freezing.