PlateUp!

Stir fry unlocks at level 15, and is the last food you'll unlock that is required to unlock all of the food related achievements, so this solution will also work for every other 'serve [x] to a customer' achievement.

You'll first need to reach level 5. If you're not there yet, you can either get runs up to franchising, then immediately scrapping the cards for xp; or you can abandon day 3 runs until you reach level 5 (I'm not sure myself which method is faster). Each card you receive is worth ~50-300xp, and you will receive that xp when the run ends. You can speed up the process by selecting the 'Abandon' option from the pause menu mid-run. The first opportunity to select a card is after completing day 3. Simply pick the card with the highest xp value, then abandon the run. Repeat until you reach level 5 and unlock the 'Autumn' environment.

The autumn environment starts every single run with a card that is worth 200xp. This allows you to abandon the run immediately after starting instead of waiting to get to day 3 each time. Simply start an Autumn restaurant with any layout/menu, then select the 'Abandon' option from the pause menu when loading in. You will receive 200xp without having to play any days, making this much quicker than any other strat that I know of. It takes ~19K xp to reach level 15 from level 5, so you will need to repeat this action ~100 times. This will take around an hour (I didn't really time myself when I did this so please let me know how long it takes you if you go for this), so get comfy and pull up a youtube video or podcast and spam autumn runs until reaching level 15.

After reaching level 15, start any restaurant with the stir fry menu option, then serve at least one customer to unlock the achievement.