Preheat the oven to 400°F (200°C). Line a baking sheet with foil or parchment for easy cleanup.
Prep the bread. Slice the loaf in half lengthwise so you have two long, flat pieces.
Place them cut-side up on the baking sheet.
Make the garlic butter. In a bowl, combine softened butter, olive oil, minced garlic, parsley, salt, pepper, red pepper flakes, Italian seasoning, and lemon zest. Mix until smooth and spreadable.
Spread evenly. Use a spatula or butter knife to coat both halves of the bread with the garlic butter mixture. Go all the way to the edges for even browning.
Bake until fragrant. Slide the tray into the oven and bake for 10–12 minutes, or until the edges start to turn golden and the garlic smells mellow and toasty.
Add Parmesan (optional). Sprinkle Parmesan over the bread and return it to the oven for 1–2 minutes to melt.
Broil for crispness. Switch the oven to broil on high for 1–2 minutes.
Watch closely. You want a deep golden top with tiny browned spots, not burnt edges.
Rest and slice. Let the bread cool for 2–3 minutes so it sets slightly. Slice into thick pieces with a serrated knife and serve warm.