Make Ahead: You can meal prep the fresh ingredients (bell peppers and red onions) for this copycat fajita veggies recipe up to 4 days before by washing, drying, and slicing them.  Just place them in an airtight container and keep them cold in the fridge. Leftovers: If you happen to have any leftovers of fajita veggies, you can place them in an airtight container in the fridge for 3 to 5 days. Freezing: You can also freeze these cooked vegetables in a freezer zip-top bag for up to one month.