Preheat your oven to 400°F (200°C). Place a baking sheet nearby for roasting.
Pat the chicken breasts dry with paper towels, then season both sides generously with salt, pepper, and thyme.
Arrange the chicken breasts on one side of the baking sheet, then scatter the sliced zucchini and squash around them.
Mince the garlic and sprinkle it evenly over the chicken and vegetables, then drizzle everything with olive oil.
Toss the vegetables gently with your hands to coat them evenly in oil and seasonings.
Place the baking sheet in the oven and roast for about 30-35 minutes, or until the chicken is cooked through and the vegetables are golden and caramelized at the edges.
Remove the sheet from the oven and let the chicken rest for 5 minutes—the juices will redistribute, keeping it tender.
Slice the chicken breasts and serve them alongside the roasted zucchini and squash, garnished with a sprinkle of fresh herbs if desired.