Education in the post-pandemic era is presented with prospects to reconfigure the mode of teaching and learning with the affordances of technology. Despite the prominence of classroom talk and its associations with students' thinking, little is known about such effects when talk is conducted in a purely asynchronous online context among students and teachers who learn English as L2. The current study explored how Hong Kong ESL learners talk and think together using a micro-blogging tool, Padlet. Twenty-five students from a HK secondary school were recruited to post their individual views on news articles before engaging in open-floor discussions about their opinions. They were then asked to write a short self-evaluation on their discussion process and evaluate their talk. The Scheme for Educational Dialogue Analysis was adopted for coding written contributions while thematic coding was adopted for oral transcriptions for analysis. Results showed that the online talk had short turn-taking and was dominated by reasoning and questioning. However, this type of online talk exposed students to a wider range of views and future learning opportunities. It also promoted the depth and breadth of their thinking and triggered internalisation of co-constructed ideas for individual production with a heightened sense of self-evaluative awareness. Based on these salient findings, the significance of learning via online talk is identified. It is also recommended that self-evaluation should be integrated in the learning process to facilitate students' interthinking.