Repeated exposure is the name of the game in language learning. However, textbooks often lack sufficient breadth of content within each unit, and finding resources that feel like a natural extension of a particular textbook is easier said than done. This workshop introduces practical ways English teachers can use generative AI to create vocabulary-based supplementary materials that align with their existing textbooks. Participants will learn prompt engineering techniques to generate level-appropriate resources using target vocabulary such as example sentences for worksheets and quizzes, dialogue scripts for speaking activities, and reading passages based on unit themes. The session will include real examples of materials created for university students in Japan, and participants will have opportunities to modify or generate their own prompts. Emphasis will be placed on designing effective and reusable instructions that yield predictable output, enabling teachers to quickly and reliably create multiple activity sets tailored to their needs. ChatGPT will be the primary tool used in this workshop, but the principles introduced here can be applied to other generative AI platforms. Participants are encouraged to bring their own devices to take full advantage of the demonstrations.