Preheat oven to 400°F with oven rack 6 inches from heat. Toss together broccoli, 1½ tablespoons of the oil, ½ teaspoon of the salt, and ¼ teaspoon of the pepper in a large bowl. Spread broccoli in a single layer on a rimmed baking sheet. Roast in oven until just tender, 20 to 25 minutes.
Meanwhile, whisk together lemon zest and juice; parsley; garlic; mustard; vinegar; honey; and remaining ½ cup oil, ½ teaspoon salt, and ¼ teaspoon pepper in a medium bowl. Set aside.
Increase oven temperature to broil; cook broccoli until slightly charred, 1 to 2 minutes. Cool about 5 minutes.
Combine broccoli, beans, baby arugula, and red onion in a large bowl. Toss with dressing; sprinkle with Parmesan.