The best way to cut veggies for fajitas is into similar-sized long strips. Strips make the fajitas easier to roll up and cutting them into similar-sized pieces allows everything to cook up in the same amount of time.  For onions, cut them in half first, and with the root end facing you, cut them into one-half-inch or larger strips going from one side to the other. Remove the seeds from bell peppers and slice them into similar-sized one-half-inch strips. If using squash, they work great cut into strips or half-coin shapes. Cut tomatoes into wedges. If using small veggies such as mushrooms that don’t cut into strips, just be sure to slice them.