Preheat oven to 425 degrees. Line a rimmed sheet pan with parchment paper.
Add the chicken pieces to the sheet pan. Brush with half of the softened butter and season with sea salt and pepper.
In a large bowl, add the remaining butter, olive oil, lemon juice and red pepper flakes. Whisk to combine.
Add the brussels sprouts, butternut squash and red onion. Toss to coat.
Arrange the vegetable mixture around the chicken pieces. Top with lemon slices.
Roast for 40 - 45 minutes until the chicken is cooked and the vegetables are browned and crunchy.
Sprinkle with grated Parmesan and serve immediately.
I used Roasted Garlic, Basil and Parsley butter by Banner Butter.