Lightly grease a sheet pan with nonstick cooking spray. Preheat oven to 400 degrees Fahrenheit.
In a small microwave-safe mixing bowl, melt 1/4 cup butter on low power in 30-second increments until melted. Whisk together with 1/4 cup olive oil, 4 cloves minced garlic2 teaspoons Italian seasoning, 1 teaspoon onion powder, 1 teaspoon salt, and 1/2 teaspoon black pepper.
Spread 1 cup cherry or grape tomatoes, 2 medium carrots, 1 medium red bell pepper, 1 medium red onion, 2 cups broccoli florets, out onto the sheet pan. Drizzle with 2/3 of the butter mixture. Roast in the 400-degree oven for about 15 minutes.
Lay the 2 sirloin steaks out onto the sheet pan, moving the vegetables to the side as needed. Drizzle with the remaining butter mixture.
Place baking sheet directly under the broiler. Broil about 4-5 minutes per side, flipping, until steak reaches desired level of doneness.
Drizzle vegetables with lemon juice and sprinkle with lemon zest just before serving. Serve hot. Season with additional salt and pepper to taste.