As an essential part of modern healthcare systems, extracting valuable insights from electronic medical records (EMRs) remains challenging due to the complexity of structured and unstructured data. Data visualization is essential for transforming complex data into comprehensible visuals that enable professionals to identify patterns and trends. This process involves selecting data attributes, transforming the data, choosing appropriate visual encoding methods, and rendering graphical representations using declarative visualization languages (DVLs). However, achieving proficiency in DVLs requires a deep understanding of domain-specific data and expertise in these languages, which poses a significant barrier for beginners and non-technical users. To address these challenges, we present HealthLens, the first user-friendly visualization tool in the EMR domain that eliminates the need for prior knowledge of DVLs. Built on the MedCodeT5 model developed by us and leveraging a large language model with a bilevel optimization approach, HealthLens enables the generation of EMR visualizations from natural language queries. This demonstrates the feasibility of creating sophisticated visualizations with minimal technical expertise, advancing accessibility in the EMR field.