Preheat oven to 425 degrees F (220 degrees C).
Into a mixing bowl, add Brussels Sprouts (1 pound), Yellow Onion (1), and Olive Oil (6 tablespoon). Season with Kosher Salt (1 1/2 teaspoon) and Ground Black Pepper (1/2 teaspoon). Toss to coat evenly.
Transfer mixture to a 9x13-inch pan. Drizzle additional olive oil over the top.
Bake for 15 minutes, shaking the pan after 10 minutes.
Give the vegetables a flip. Add Cherry Tomato (1 cup) and drizzle additional olive oil over top. Toss to combine.
Bake for another 15 minutes, shaking the pan once or twice throughout.