A prism-based self-injection locked seamlessly tunable blue InGaN/GaN laser diode composite cavity system is presented. A rigorous analysis of this external cavity diode laser (ECDL) system is performed at two different optical feedback powers. At 130 mA low injection, the high reflection system (HRS) exhibits a record wideband tuning span of ~12.11 nm with a side-mode-suppression-ratio (SMSR) ≥ 15 dB, measuring as high as 40 dB, linewidth ≤ 110 pm, and a working power of about 3 mW. Whereas, a tuning range of 8 nm with linewidth ≤ 88 pm, SMSR ≥ 13 dB, reaching a maximum of 35 dB with 14.5 mW usable power is achieved from the low reflection system (LRS) at the same injection current. Moreover, an inverse relationship between the optical power and the tunability is observed in both the systems with a value as high as 180 mW exhibited by LRS configuration and attaining a tunability of 4.5 nm. Both systems highlight high stability even at higher injection currents and temperature. Such a robust, simple, and compact system may serve as a crucial light source in a plethora of diverse applications besides visible optical communications. To the best of our knowledge, this is the first report on a continuously tunable self-injection locked tunable laser system.