01 - Preheat oven to 425°F. Line a large sheet pan with parchment paper or lightly grease it.
02 - Pat chicken breasts dry with paper towels. Rub with olive oil, salt, and pepper. Arrange in the center of the sheet pan.
03 - Scatter pineapple chunks, bell peppers, and red onion wedges around the chicken on the pan.
04 - In a small bowl, whisk together soy sauce, honey, rice vinegar, garlic, ginger, tomato paste, and red pepper flakes if using.
05 - In a separate small bowl, mix cornstarch with water until smooth. Stir into the sauce mixture until fully incorporated.
06 - Drizzle half of the sauce over the chicken and vegetables. Reserve the remaining sauce for serving.
07 - Bake for 20 minutes until chicken begins to brown and vegetables start to soften.
08 - Remove from oven, brush chicken with more sauce from the pan, and toss vegetables gently to coat.
09 - Return to oven and bake another 8-10 minutes, until chicken reaches internal temperature of 165°F and vegetables are tender.
10 - Let chicken rest for 5 minutes. Slice and serve with roasted pineapple and vegetables. Drizzle with remaining sauce and garnish with cilantro, sesame seeds, and green onions if desired.