01 - Preheat your oven to 400°F (200°C). In a substantial mixing bowl, combine the baby potatoes, carrots, red bell pepper, and red onion. Toss with olive oil, 1/2 teaspoon salt, and 1/4 teaspoon black pepper until evenly coated. Transfer the seasoned vegetables to a large baking sheet lined with parchment paper, spreading them in a single layer.
02 - In a separate small bowl, whisk together the Dijon mustard, whole grain mustard, honey, fresh lemon juice, minced garlic, dried thyme, and the remaining salt and black pepper until well combined.
03 - Arrange the chicken breasts on top of the prepared vegetables on the baking sheet. Generously brush half of the prepared honey mustard glaze over the chicken.
04 - Place the baking sheet into the preheated oven and roast for 20 minutes. Carefully remove the baking sheet. Brush the chicken with the remaining honey mustard glaze and gently stir the vegetables to ensure even cooking and caramelization.
05 - Return the baking sheet to the oven and continue to bake for an additional 15 minutes, or until the chicken is thoroughly cooked through (internal temperature should reach 165°F/74°C) and the vegetables are tender and slightly browned. Allow the dish to rest for 5 minutes before serving.
06 - Garnish the finished dish with freshly chopped parsley and serve immediately.