Sideris founded the Tashas Group in 2005 after having previously worked in and owned franchised restaurants. The group has 10 concepts, including Flamingo Room by tashas, Avli by tashas, Le Parc by tashas, Galaxy Bar, Bungalo34, and tashas café across 35 locations in the U.A.E., South Africa, and the U.K. It plans to inaugurate The Academy, a hub for F&B and service training, in Dubai in September 2024, alongside Nala, a quick-service restaurant. Sideris works with her brother Savva, who joined the group in 2008. She has also authored two cookbooks: tashas Café Classics and tashas Inspired, which were published in 2015 and 2020, respectively.