Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Scrub the sweet potato and dice into 1/2-inch cubes, then thinly slice the red and green bell peppers.
Remove the tough stems from the shiitake mushrooms and slice the caps into thick strips.
Peel the shallot and slice it into thin rings, and cut the chicken breast into uniform 1-inch pieces.
Place the chicken, sweet potatoes, peppers, mushrooms, and shallots onto the prepared baking sheet.
Drizzle with extra virgin olive oil and sprinkle evenly with sea salt, black pepper, dried thyme, and garlic powder.
Toss everything thoroughly with your hands or tongs to ensure an even coating of oil and spices.
Spread the mixture into a single layer, ensuring the chicken and vegetables aren't overcrowded so they roast rather than steam.
Roast for 20 to 25 minutes, tossing the ingredients halfway through, until the chicken is cooked through and the potatoes are golden and tender.