Preheat oven to 350 degrees F.
Place the halved and sliced half-circle pieces onto a large baking sheet.
Drizzle olive oil over the sliced summer squash, sprinkle with garlic powder, and season to taste with kosher salt and black pepper. Toss to coat all the summer squash pieces evenly.
Roast in the oven for 45-60 minutes or until summer squash is cooked through and lightly browned on some edges. Turn the summer squash a couple of times while roasting for even cooking.
Place the cooked summer squash into a serving bowl. Taste and adjust seasoning if needed.
If making ahead, the summer squash can be refrigerated at this point and either reheated just before serving or served chilled.
Just before serving, add the chopped fresh basil to the top serving bowl and toss to distribute it evenly.
Serve immediately.