A number of smartphone apps have been developed in recent years to help people cope with stress and promote mental well-being. Such apps have attracted significant attention in current research. However, interaction design issues, such as usability and user experience, have so far been relatively unexplored. This paper presents a meta-analysis of studies of mobile apps for stress management and mental well-being, specifically focusing on interaction design issues. Through a scoping literature search we selected the total of 46 articles, published in the last decade, for qualitative in-depth analysis. The analysis reveals that the main interaction design issues addressed in the papers are ease of use, user engagement, and privacy. Key opportunities and challenges for future work are discussed.