Preheat oven to 375°F. Boil green beans 4-5 minutes until crisp-tender; drain and set aside.
Melt butter in a skillet over medium heat. Add garlic and cook 30-45 seconds until fragrant.
Stir in cream and broth; simmer 2-3 minutes until slightly thickened. Remove from heat.
Mix in 3/4 cup Parmesan, lemon zest, salt, and pepper. Toss sauce with green beans in a baking dish.
Combine panko and remaining 1/4 cup Parmesan; sprinkle over beans.
Bake 15-18 minutes until topping is golden and sauce bubbles. Let rest 5 minutes before serving.