In this study we examined how the introduction of a parallel finger-tapping task influences second language speech (L2) encoding mechanisms and monitoring processes and how the level of proficiency impacts the efficiency and accuracy of L2 performance under single and dual task conditions. The results indicated that imposing dual task demands has a negative effect on the accuracy of lexical selection and the efficiency of error-correction processes. We argue that this can be explained with reference to attentional bottleneck effects on lexical selection processes and on monitoring. The findings also revealed that the level of L2 competence influenced both the speed and the accuracy of speech encoding processes and the efficiency of monitoring.