Enhancing students' lexical fluency and academic performance in speaking exams presents a significant challenge for English as a foreign language (EFL) instructors. The pursuit of effective tools to engage students and facilitate their learning process has been ongoing. The incorporation of technology in EFL learning contexts, particularly through learning-oriented assessments, offers a promising solution to the traditional difficulties of vocabulary acquisition in the classroom. Research indicates that Mobile-Assisted Language Learning (MALL) not only streamlines the learning process but also boosts student motivation and participation. In light of the challenges faced in improving the speaking exam performance of students in foundation programs in Oman, a study was conducted to assess the impact of Mentimeter, a Student Response System, on student engagement, vocabulary recall, and speaking proficiency. The study involved 275 students from a public university in Oman who participated in Mentimeter quizzes designed to measure the platform's effect on vocabulary retention, lexical fluency, and overall speaking performance. Additionally, the study explored teachers' perceptions of the integration of Mentimeter as a formative assessment tool. The findings underscore the significance of MALL in enhancing learning-oriented assessment in EFL classrooms and provide insights for educators on utilizing such technologies to bolster vocabulary retention and speaking skills.