Melt butter with olive oil in a small saucepan.
Remove off of the heat and grate in the garlic and lemon zest. Next, squeeze in the juice from half a lemon and measure and add in the Italian seasoning, salt and pepper and crushed red pepper flakes if using. Stir to combine and set aside.
Place the zucchini halves onto a rimmed metal sheet pan. Using a paring knife, score x's into the flesh before brushing with some of the butter mixture.
Preheat your grill to 400° to 500°. Once hot, place the zucchinis onto the grill grates, cut-side down, close the lid and grill for 8 to 10 minutes or until grill marks form.
Turn, brush with the remaining butter mixture making sure the garlic, zest and herbs are worked into the score marks.
Sprinkle the parmesan over top, cover and grill for 1 to 2 more minutes or until the cheese melts.
Serve immediately with fresh basil leaves scattered overtop.
