Preheat oven to 350°F (175°C).

Spray a 9-inch pie plate with cooking spray.

In a large skillet, brown the ground beef over medium-high heat. Drain off any excess grease.

Add the chopped onion to the skillet and cook until softened, about 5 minutes.

In a bowl, whisk together the eggs, Bisquick mix, salt, and milk until smooth.

Stir in the cooked beef and onion mixture and half of the shredded cheddar cheese.

Pour the mixture into the prepared pie plate and top with the remaining cheddar cheese.

Bake for 30-35 minutes, or until the pie is set and golden brown.