Step 1: Heat the oven and prepare the pan - Set your oven to 400 degrees Fahrenheit so it has plenty of time to get hot while you prepare dinner. Line a medium or large sheet pan with parchment paper, then set it nearby. The parchment paper is not absolutely required, but I use it every time because it keeps the vegetables from sticking and makes cleanup feel almost unfairly easy.
Step 2: Cut the chicken and vegetables evenly - Cut the chicken breast into 1 inch pieces, then chop the broccoli, bell peppers, carrots, and red onion as directed. Halve the baby potatoes so they can roast through without taking forever. This step may feel like the longest part of the recipe, but a few extra minutes of even chopping makes a huge difference when the pan goes into the oven. You want the chicken and vegetables to finish at roughly the same time, not have one lonely potato still hard in the middle while everything else is ready.
Step 3: Build the ranch and sriracha coating - Add the chicken, broccoli, bell peppers, carrots, red onion, and potatoes to a large bowl. Pour in the olive oil, then add the sriracha, minced garlic, ranch seasoning, salt, and pepper. Use a large spoon or clean hands to toss everything together until the chicken and vegetables are evenly coated. Take a second to look through the bowl before moving on. You want to see seasoning on the potatoes and vegetables too, because those little bits of ranch and garlic are what make the whole meal taste connected.
Step 4: Spread everything into one even layer - Pour the seasoned chicken and vegetables onto your prepared sheet pan. Spread everything into a single, even layer, making sure the potatoes are cut side down whenever possible. Give the ingredients a little breathing room rather than piling them into the middle of the pan. When the food is spread out, it roasts and browns. When it is crowded, it steams. Roasted edges are where the good stuff happens.
Step 5: Roast until tender and cooked through - Place the pan in the oven and roast for 22 to 25 minutes. Around the halfway point, you can carefully stir everything with a spatula if you want more even browning, though it will still turn out well if you leave it alone. The chicken is ready when the thickest pieces reach 165 degrees Fahrenheit, the potatoes are fork tender, and the broccoli has soft stems with a few browned tips. Your kitchen should smell garlicky, tangy, and just a little spicy by now.
Step 6: Rest briefly and serve hot - Let the sheet pan sit for about 3 to 5 minutes after it comes out of the oven. That short rest gives the chicken time to settle and keeps everyone from burning their mouths because dinner smelled too good to wait. Spoon it straight onto plates, making sure each serving gets chicken, potatoes, and plenty of colorful vegetables. A little extra sriracha on the table is always welcome for anyone who likes more heat.