We have studied the formation of vapour bubbles in a microchannel, a confined quasi-two dimensional system where one dimension is much smaller than the other two. The bubble is created by thermocavitation, i.e. by overheating a small region of the fluid, using a continuous wave laser diode. To the best of our knowledge, this is the first time that thermocavitation is achieved with such low power light sources (∼ 100mW). Our fast-imaging experimental results are compared with theoretical models and show good agreement with the predicted bubble growth. Considering the bubble as a piston able to transfer kinetic energy to the fluid, we show that this microfluidic system is a low-cost micro-engine able to convert thermal energy into work.