Balsamic Chicken with Leeks and Peppers

uncooked onion(s)

1 medium, cut into wedges

uncooked leek(s)

2 medium, trimmed and sliced

sweet red pepper(s)

1 medium, sliced in half, stem and seeds removed

yellow pepper(s)

1 medium, sliced in half, stem and seeds removed

olive oil

2 tsp

rosemary sprig

2 item(s)

table salt

⅛ tsp, or to taste

black pepper

⅛ tsp, or to taste

uncooked boneless skinless chicken breast(s)

1¼ pound(s), four 6 oz pieces

balsamic vinegar

1 Tbsp