Step 1: Preheat the Oven - Set your oven to 400 degrees and grease a large baking sheet. I like to do this first because once the oven is hot, everything moves along smoothly. A greased pan helps the potatoes release more easily and makes cleanup a whole lot nicer. You want enough room for the ingredients to spread out, because crowded vegetables steam instead of roast.
Step 2: Coat the Chicken in Pesto - Cut the chicken into pieces about 1 to 1 ½ inches wide, then place it in a medium bowl with the pesto. Stir until every piece is coated. Cover the bowl and put it in the refrigerator while you prep the vegetables. It is not a long marinade, but even that short rest gives the pesto a little time to cling to the chicken. That means more flavor in every bite.
Step 3: Prep the Potatoes and Broccoli - Cut the Yukon gold potatoes into 1 ½ inch pieces and cut the broccoli into small florets. Add them to a large bowl with the olive oil, Italian seasoning, garlic powder, salt, and pepper. Toss everything until the vegetables are coated. This step matters because seasoning in the bowl gives you better coverage than sprinkling everything after it is already on the pan.
Step 4: Start Roasting the Vegetables - Spread the potatoes and broccoli on the prepared sheet pan in an even layer. Put the pan in the oven and bake for ten minutes. Starting the vegetables first gives the potatoes time to soften before the chicken goes on the pan. That way the chicken stays juicy and the potatoes are not still firm when dinner hits the table.
Step 5: Add the Chicken and Tomatoes - After ten minutes, pull the pan from the oven and carefully add the pesto marinated chicken and cherry tomatoes. Spread everything out as evenly as you can. Try to keep the chicken pieces from piling on top of each other. The tomatoes can tuck into the open spaces. They will roast down and release a little juice, which mixes beautifully with the pesto and seasoning.
Step 6: Finish Baking Until Tender - Return the sheet pan to the oven and bake for twenty to twenty five minutes, or until the chicken is cooked through and reaches 165 degrees in the center. The potatoes should be tender when pierced with a fork, the broccoli should have roasted edges, and the tomatoes should look soft and glossy. Let the pan rest for a few minutes before serving so the juices settle back into the chicken.