Preheat grill on medium-high. In a large bowl, toss zucchini with oil, lemon zest, and red pepper flakes. Season with salt and pepper.
Once grill is hot, carefully use tongs to rub an oiled paper towel over grates.
Using tongs, place zucchini on grill. Cover and cook, 3 minutes. Flip and continue cooking on high, covered, 2 to 3 minutes more.
When zucchini is tender, remove from heat and garnish with basil and more red pepper flakes.