Preheat oven to 400°F. Coat a large sheet pan with olive oil or line with parchment.
Add the mushrooms, bell pepper, zucchini, and frozen cauliflower gnocchi to a bowl.
Drizzle with 1–2 tablespoon olive oil, season with salt and pepper, and toss.
Spread evenly on the sheet pan and roast for 10 minutes.
In a separate bowl, toss the sliced chicken sausage and whole cherry tomatoes with the remaining olive oil, salt, pepper, and red pepper flakes (optional).
After 10 minutes, remove the sheet pan and add the sausage + tomatoes.
Return to the oven for 20 minutes, stirring halfway, until everything is golden and cooked through.
Remove from the oven and drizzle the pesto over the hot vegetables and sausage.
Toss gently until coated (you can thin the pesto with a splash of olive oil if you want a lighter drizzle).
Top with parmesan and serve warm.