This paper presents a tunable liquid lens (TLL)-assisted indoor mobile visible light communication system. To mitigate performance degradation caused by user mobility and random receiver orientation, an electrowetting cuboid TLL is used at the receiver. By dynamically controlling the orientation angle of the liquid surface through voltage adjustments, signal reception and overall system performance are enhanced. An accurate mathematical framework is developed to model channel gains, and two lens optimization strategies, namely ($i$) the best signal reception (BSR), and ($ii$) the vertically upward lens orientation (VULO) are introduced for improved performance. Closed form expressions for the outage probability are derived for each scheme for practical mobility and receiver orientation conditions. Numerical results demonstrate that the proposed TLL and lens adjustment strategies significantly reduce the outage probability compared to fixed lens and no lens receivers across various mobility and orientation conditions. Specifically, the outage probability is improved from $1\times 10^{-1}$ to $3\times 10^{-3}$ at a transmit power of $12$ dBW under a $8^{\circ}$ polar angle variation in random receiver orientation using the BSR scheme.