In a small bowl, whisk together olive oil, lemon juice and zest, honey, a pinch of salt, and pepper to taste until smooth.

Chop romaine lettuce into bite-sized pieces and place in a large salad bowl. Add the sliced red onion.

Sprinkle the parmesan cheese and crushed red pepper flakes into the salad bowl, then toss gently to combine.

Drizzle the dressing over the salad mixture and toss to coat the ingredients evenly.

Serve immediately while the lettuce is crisp.