Preheat oven to 425°F. On a large sheet pan, toss bell peppers, onion, and pineapple with olive oil, salt,and pepper. Add marinated chicken and spread in a single layer.
1 red bell pepper, 1 yellow bell pepper, 1 red onion, 1 ½ cups pineapple chunks, 1 tablespoon extra virgin olive oil, ½ teaspoon fine sea salt, ½ teaspoon fresh ground black pepper