Step 1: Heat the Oven and Prepare Your Pan - Preheat your oven to 425 degrees Fahrenheit. You want the oven fully hot before the sheet pan goes in because that stronger heat helps the potatoes brown instead of simply becoming soft. Grab a medium sheet pan and give yourself enough room to spread everything out. If the ingredients are piled tightly on top of one another, they will release steam and you will miss some of those browned edges that make the potatoes especially good.
Step 2: Chop the Chicken, Potatoes, and Onion - Cut the potatoes into roughly 1 inch pieces, chop the red onion, and cut the chicken breasts into bite sized pieces. Try to keep the chicken pieces fairly similar in size so one piece is not dry by the time a larger one cooks through. I do the same with the potatoes. Nobody needs to get out a ruler, but keeping everything reasonably uniform makes the whole pan cook more predictably.
Step 3: Arrange Everything on the Sheet Pan - Place the potatoes and chopped red onion on one side of the sheet pan and arrange the chicken on the other side. Keeping the two sections separate makes the final steps easier and allows you to toss each side without sending raw chicken juices through the vegetables. Drizzle the olive oil over everything, then sprinkle on the garlic powder, onion powder, paprika, salt, and black pepper. Use tongs or a spatula to toss the chicken and vegetables separately until everything has a light, even coating.
Step 4: Roast the First Fifteen Minutes - Slide the pan into the hot oven and roast everything for 15 minutes. This first stretch gives the potatoes time to soften and lets the chicken begin cooking while the onion starts turning tender around the edges. You do not need to hover over it. This is usually when I wipe down the cutting board, put away the seasonings, or deal with whatever small household emergency has appeared since dinner went into the oven.
Step 5: Toss and Finish Roasting - After 15 minutes, carefully remove the pan and toss the potatoes, onions, and chicken, still keeping the chicken mostly on its own side. Return the pan to the oven for another 10 minutes. The chicken should be fully cooked and the potatoes should be tender when pierced with a fork. If your potato pieces were slightly larger, they may need a few extra minutes, so judge by tenderness rather than rushing them out of the oven.
Step 6: Add the Buffalo Sauce and Blue Cheese - Once everything is cooked, drizzle the Buffalo sauce over the chicken and gently toss until the pieces are coated. Then drizzle the blue cheese dressing across the chicken, potatoes, and onion. I like keeping some streaks of dressing visible instead of mixing everything completely because you get bites that are spicy, bites that are creamy, and bites where the two meet right in the middle.
Step 7: Garnish and Bring It to the Table - Finish the pan with the diced green onions and serve while everything is still warm. I usually put extra Buffalo sauce and dressing on the table so everybody can adjust their own plate. That tiny bit of flexibility goes a long way with family meals, especially when one person loves heat and another thinks black pepper is an adventure.