Preheat oven to 425°. Spray large rimmed baking pan with cooking spray; spread onion on pan and spray with cooking spray. Roast onion 10 minutes.
In wide, shallow dish, stir mustard, lemon juice and butter. In large zip-top plastic bag, mix breadcrumbs, cheese and ¼ teaspoon pepper. In batches, dip chicken in mustard mixture to coat; add to breadcrumb mixture in bag and toss to coat.
Push onion to 1 side of pan; spray opposite side of pan with cooking spray. Stir artichokes and tomatoes into onion; spread chicken on opposite side of pan. Spray chicken and vegetables with cooking spray.
Roast 10 minutes or until bottom of chicken browns; turn chicken and stir vegetables. Roast 15 minutes longer or until internal temperature of chicken reaches 165°. Serve chicken and vegetables garnished with thyme sprigs and lemon wedges, if desired.
Serving Size 1
Servings 0
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.