These mixed vegetable fajitas are easy, hearty, and healthy. They use multiple kinds of vegetables and lots of seasoning, making this an easy choice for a quick dinner. What You Need to Make Them To make these fajitas you’ll need things like onions, bell peppers, and some seasoning. Onion I like using yellow onion for this, but you can probably use any variety. Red onions may be a bit strong, but I can see them working in this as well. Bell Pepper For the peppers, I recommend