Explore locations: Explore specific locations in the game, such as the grocery store or blacksmith shop in Mondown, and you may find a recipe for grilled fish.
Complete the task: Complete specific tasks in the game, such as talking to NPC or completing certain challenges, which may reward the recipe of grilled fish.
Store purchase: check the menu options available in the in-game store, and use in-game currency or other specific trading methods to purchase the required recipes.
If none of the above methods can get Mond's grilled fish recipe, you can try to search for other players' strategies online or ask other players for advice.