Rinse and drain black beans.

Mash black beans in a bowl using a fork.

Add cooked brown rice, finely chopped onion, lightly beaten egg, and 2 tablespoons of salsa to the mashed beans.

Mix the ingredients well.

Season with salt and pepper to taste.

Coat a large nonstick skillet with cooking spray.

Drop the bean mixture by 1/2 cupfuls into the skillet.

Flatten each portion to 1/2-inch thickness.

Cook over medium heat for 4-5 minutes on each side, or until firm and browned.

In a small bowl, combine reduced-fat sour cream and the remaining 1/4 cup of salsa.

Split hamburger buns.

Place a lettuce leaf on the bottom bun.

Add a burger patty.

Top the burger with the sour cream and salsa mixture.

Add a slice of reduced-fat cheddar cheese.

Cover with the top bun and serve.