The paper discusses a novel architecture proposed within the scope of the ongoing MonB5G EU-funded project. Considering a multiplicity of challenges towards realizing an effective network slice management in modern 5G networks, our work considers explicitly the context promoted by the Zero-touch network and Service Management (ZSM) framework, assessed as an indispensable part of next-generation management systems. MonB5G focuses upon the provision of scalable and automated management and orchestration of high numbers of parallel network slices, as envisioned in 5G and beyond. Within this scope, we propose a detailed architecture composed of static and dynamically deployed components. Altogether, they support operations related to slicing orchestration, fault management (self-healing), self-configuration, performance optimization (including energy saving), and security-related operations of slices. In the paper, we identified each separate architectural layer and explained all involved modules and interfaces. The proposed framework is able to support the deployment of a massive number of slices in different administrative and technological domains. Furthermore, the potential extensions and/or enhancements of the architecture are also proposed and assessed.