This qualitative documentary research reports a comprehensive analysis that unveils a colonial research tension and emergent decolonial research trends found in the Masters Program in Education at a Colombian private university, Universidad Externado de Colombia, during the period 2015-2023. The dataset comprised 81 theses and 19 research reports produced by in-service teachers as a graduation requirement for the program. Our study included two core moments: first, a heuristic one centred on systemising from the theses and research reports, and second, a hermeneutic moment focused on our critical analysis of data gathered from the theses and research reports. Findings brought to light the current state of in-service teachers' research practices, revealing a colonial research tension that entails a hegemony of action research. Also, results unveiled emergent decolonial research trends that are casting doubt on pervasive instrumental language skills-oriented research, illustrating an ongoing transition from descriptive to critical emancipatory research objectives, and subverting instrumental and decontextualised pedagogical interventions that reproduce and naturalise dominant cultures and knowledge. Results compel teachers to conduct research from a critical standpoint by inquiring into English language teaching (ELT) ideology, mechanisation of grammar and foreign teaching methods, instrumentalisation of research, and subordination of participants.