Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Cut the chicken breast into bite-sized 1-inch cubes and place them in a large mixing bowl.
Chop the broccoli into small florets, dice the red bell pepper and yellow squash, and slice the red onion into wedges.
Add all the vegetables to the bowl with the chicken.
Drizzle the olive oil over the mixture and sprinkle with dried oregano, dried thyme, sea salt, and black pepper.
Toss everything thoroughly until the chicken and vegetables are evenly coated with the oil and herbs.
Spread the mixture in a single layer on the prepared baking sheet, ensuring nothing is overcrowded so it roasts rather than steams.
Roast in the oven for 20 to 25 minutes, or until the chicken is cooked through and the vegetables are tender and slightly caramelized.
Remove from the oven and drizzle with fresh lemon juice before serving.