Preheat the oven to 360F / 180C and line a baking sheet with parchment paper.
Scatter the cauliflower florets, broccoli florets, red bell pepper pieces and baby corn onto the baking sheet, drizzle with olive oil and sprinkle over the thyme and salt. Toss to coat the veggies. Roast for 20-25 minutes or until you have the level of browning you like.
While the vegetables are roasting, add the cubed potatoes to a large pot and cover with water so there is a few inches of water above them. Add a good pinch of salt. Bring to a boil, then reduce the heat and cook at a light simmer for about 20 minutes. They should be soft and fork tender. Cook for a few more minutes, if required.
Drain the potatoes in a colander and tip them back into the pot. Pour in the milk, and add the butter, thyme and salt. Use a potato masher to mash to the texture of mashed potatoes you like.
Slice your chicken breasts into two pieces of an equal thickness, lengthways. Pat dry with paper towel. Sprinkle over salt, black pepper and garlic powder (you can also add herbs or spice, to preference). Heat the oil in your skillet and, once hot, cook the chicken breasts for 3-4 minutes each side. Check for an internal temperature of 165F using a meat thermometer at their deepest point.
Shred the chicken using two forks or in a stand mixer with the appropriate attachment.
Make the tahini dressing by combining tahini, water and maple syrup in a small bowl. Whisk or stir to a sauce consistency, adding more tahini to thicken and more water to thin, to preference.
Spoon the mashed potatoes into your bowls, then top with the shredded chicken and roasted vegetables. Drizzle over the tahini sauce, if using, and scatter over some fresh parsley. Season with salt and black pepper, to taste preference.