These don't really have much of a "recipe". They are so versatile, you can pretty much just use whatever you have on hand. That's what I love about Mexican food! For some reason, everything just goes together so well. Here's what we used last night, but feel free to change it up as you prefer.
First of all, tortillas. We used these green-colored, jalapeno and cilantro tortillas that were really yummy and gave it an extra kick. Regular ones work just as well, but that's why the color is off in the picture.
For the filling:
1 can of black beans drained and rinsed, then heated up in the microwave
1/2 of a yellow bell pepper (just because it was in the fridge and needed to be used)
spinach (put on after the picture was taken)