Preheat the oven to 400 degrees and grab a large sheet pan.
In a small bowl or mason jar mix the seasonings: chili powder, oregano, salt, cumin, onion powder, black pepper. Set aside.
Place the cut onions, peppers and chicken on the sheet pan. Drizzle with oil and sprinkle on the seasoning mixture. With clean hands, toss the pepper and chicken mixture so the seasonings and oil are distributed evenly.
Place in the oven for 20 minutes.
Meanwhile make the cilantro lime vinaigrette by placing all the ingredients into a mason jar (or bowl), pop the lid on and shake vigorously until the ingredients are emulsified together (or whisk if using a bowl). Set aside.
Pull the sheet pan out of the oven and add the rinsed pinto beans and halved tomatoes, place back in the oven for 5 minutes.
Drizzle the sheet pan fajitas with the cilantro lime vinaigrette and serve.