Ground Beef Shepherd's Pie

Step 1
Preheat the oven to 350 degrees F (175 degrees C). Grease a 2-quart casserole dish with cooking spray.

Step 2
Heat oil in a large skillet over medium heat. Cook and stir onion in hot oil until translucent, about 5 minutes. Add ground beef and basil. Cook and stir until beef is crumbly and browned, about 5 minutes. Mix in green beans, tomatoes, and garlic; cook until beans are slightly softened, about 5 minutes more. Transfer to the prepared casserole dish.

Step 3
Mix together mashed potatoes, water, and beaten egg in a medium bowl until smooth. Spread evenly over beef mixture.

Step 4
Bake in the preheated oven until potatoes start to brown on top, 15 to 20 minutes. Sprinkle with cheese and continue baking until cheese is melted, about 5 more minutes.