Heat the oven to 425°F. Line two baking sheets with parchment paper.

Combine the onion, broccoli, and bell pepper in a mixing bowl with half the garlic; add 1 tbsp olive oil, 1 tsp italian seasoning, 1/2 tsp salt, and 1/4 tsp pepper. Toss until the vegetables are evenly coated. Spread the vegetables onto a prepared baking sheet, and shake to distribute into an even layer. Transfer to the oven and roast 10 minutes.

Combine the yellow squash, zucchini, and cherry tomatoes in the mixing bowl along with the garlic and remaining olive oil, italian seasoning, salt, and pepper. Toss until the vegetables are evenly coated. Spread the vegetables onto the second prepared baking sheet, and shake to distribute into an even layer.

When the timer goes off, remove the first sheet pan from the oven, stir the vegetables, then return both sheet pans to the oven. Roast an additional 10 minutes, or until the vegetables are bite-tender and starting to caramelize.

Transfer the roasted vegetables to a serving bowl and gently toss to combine. Garnish with fresh basil and serve immediately.