If you are including rice/quinoa in this meal, start it before doing anything else, using your preferred cooking method. If you're new to cooking these grains, click here for rice cooking instructions and here for quinoa cooking instructions.
Slice the peppers and onions into thin strips and mushrooms or zucchini into slices.
In a wide skillet, heat a small splash of cooking oil over medium-high heat and add the veggie strips and a pinch of salt and pepper. Allow them to blacken a little bit, stirring occasionally, for about 10 minutes. I like to sprinkle a little bit of cumin, chili powder, or taco seasoning on them, but don't go overboard.
While the veggies are cooking, prepare the rest of the components and put them into individual bowls for serving.
Rinse and drain the beans. (I usually don't bother to heat or season them, but you can if you wish)
Chop the remaining garnishes.
Set out bowls or containers with serving spoons if doing a burrito bowl bar.