The fifth-generation (5G) of mobile networks and beyond is to host a variety of services for industry verticals with a diverse range of requirements. Network slicing (NS) is considered to be the fundamental enabling technology to address legacy networks' shortcoming, by tailoring logical virtual networks, called network slices, over the same infrastructure. Adopting the concepts of virtualization and open interfaces, Virtual radio access networks (vRAN) and Open RAN (ORAN) are two of the most promising architectures proposed for slicing radio access networks. To realize the efficient deployment (i.e. increase flexibility, scalability ,and decreased CAPEX and OPEX) of these architectures, a proper network planning approach is essential. This paper introduces a novel approach to planning and design of the ORAN architecture that takes into account QoS, CAPEX, OPEX and the transport network, simultaneously. The ORAN slice planning and design is formulated as a multi-objective optimization with binary variables and solved by simulated annealing.This paper provides a comprehensive discussion of the results. The proposed approach can be used in designing 5G ORAN network slices but also can be used as a transition network solution to integrate the 4G tier together with 5G for enabling a smooth and less costly transition.