Preheat the oven to 425 degrees and place one oven rack on the top third of the oven and the other on the bottom third. Line two baking sheets with parchment paper or spray them with nonstick cooking spray.
Put the chicken breast on one of the baking sheets, sprinkle it with 1/8 tsp. of the salt and pepper, drizzle it with ½ tsp. of oil, and put it into the oven (you don’t need to wait for the oven to fully preheat). Bake it for 20 - 25 minutes, or until cooked through.
Meanwhile, in a large bowl, toss the zucchini with the remaining oil. Spread the zucchini evenly on the second baking sheet and roast it on the other oven rack for 10 - 12 minutes, or until some pieces are just starting to brown.
While the zucchini is roasting, dice or shred the chicken and put it and the beans into a large bowl along with the chili powder, cumin, and remaining salt and pepper. Stir well. When the zucchini is roasted, mix it into the black bean, chicken, and spice mixture.
Lay out the tortillas. Put about ¼ cup of the bean mixture in the center of each tortilla. Evenly distribute the cheese on top. Fold each tortilla as you would a burrito (first fold in the sides and then roll up the tortilla) and place seam-side down on one of the baking sheets you used for the chicken or zucchini, spraying more cooking spray or using new parchment paper if the food got at all burnt on.
Lightly spray each chimichanga with the cooking spray (if using), to give them a nice crust and a golden color.
Bake for 15 - 18 minutes, or until golden on top. Serve immediately with a dollop of sour cream and/or a scoop of salsa, if desired. Refrigerate for up to 3 days, or freeze for up to 3 months.