Place the chicken in the middle of a baking sheet or roasting pan (without the rack). Arrange the baby potato, carrots, and red onion around the chicken.
Drizzle olive oil all over the chicken and vegetables - make sure at least 1 tablespoon is just on the chicken. Sprinkle everything with dired rosemary, salt, and pepper.
Roast for 50-60 minutes. Check the vegetables at the 30-minute mark to make sure they're not getting too browned. If they are, add some water or chicken broth to the pan. Once the chicken breast has an internal temperature of 165 degrees F the bird is cooked through.
Remove the baking sheet fom the oven and let rest for 15 minutes. Then transfer the chicken to a cutting board and carve it. Plate the chicken along with some of the roasted vegetables. Serve warm.
Notes
Nutritional information includes chicken and veggies.