Help with Structuring .Net Web API project and Implementing SOLID Design Principles

I have set up a small Web API project in .Net which has got different layers like Service / Business and Data Layers. I have implemented some SOLID Design principles and also used Unity to achieve DI.

I have also added some Unit Tests but Dependencies are not mocked in tests.

I am looking for someone who has got solid software engineering experience using SOLID principles and can review my code and help with mocking dependencies in tests.