Pre-service Indonesian Language Education (Pendidikan Bahasa dan Sastra Indonesia/PBSI) teachers often struggle to translate instructional-design theory into contextually grounded, creative lesson designs. Building on evidence of a broader theory-practice gap in Indonesian pre-service language teacher education, this study examined whether this gap is compounded by underdeveloped metacognitive regulation (planning, monitoring, evaluating) among fourth-semester PBSI students enrolled in the Indonesian Language and Literature Learning Studies course at Universitas Muhammadiyah Pringsewu (UMPRI). The study aimed to develop, validate, and empirically test the GenAI-Prompting Learning Model (GPLM), a four-level structured prompting framework (Exploratory, Analytical, Synthetic, and Evaluative Prompting) designed to support students' metacognitive regulation during instructional-design tasks. An embedded mixed-methods Research and Development (R&D) design was used, operationalized through the five ADDIE stages (Analyze, Design, Develop, Implement, Evaluate); qualitative data were nested within a pre-experimental one-group pretest-posttest quantitative design and used to explain the numerical findings. The GPLM was reviewed by three expert validators (two language-pedagogy specialists and one educational-technology specialist) and implemented with 41 fourth-semester PBSI students (28 female, 13 male) over a 14-session/14-week intervention. Instruments comprised the Metacognitive Skills Test (MST), the Instructional Design Quality Rubric (IDQR), a 15-item GPLM Practicality Questionnaire, observation sheets, digital prompting journals, and semi-structured interviews with 15 purposively selected students. Content validity, calculated with Lawshe's (1975) Content Validity Ratio across three validators, reached 0.99; because CVR critical values are conventionally tabulated for panels of five or more raters, this result is reported with the underlying calculation and interpreted as indicative rather than definitive evidence of content validity. Thematic analysis of interviews and journals identified three explanatory themes-externalization of internal thought, iterative refinement through dialogic interaction, and emerging epistemic agency. The findings showed that the GPLM is a well-received, promising instructional tool associated with improved metacognitive and instructional-design scores, rather than as proof of a causal "acceleration" effect.