Preheat oven to 450°F (232°C).

In a large skillet, brown ground beef and chopped onion over medium heat, breaking up the beef until it's crumbly.

Cook for 8 to 10 minutes, or until the beef is no longer pink.

Pour off any excess drippings from the skillet.

Season the beef mixture with salt.

Add prepared chunky salsa and drained chopped green chilies to the beef mixture.

Stir in the shredded cheddar cheese or Colby-Monterey Jack cheese.

Spoon about 1/4 of the beef mixture onto one half of each flour tortilla.

Fold the tortilla in half to close, forming a quesadilla.

Arrange the folded tortillas on two baking sheets that have been sprayed with vegetable oil cooking spray.

Lightly spray the tops of the tortillas with cooking spray.

Bake in the preheated oven for 8 to 10 minutes, or until the tortillas are lightly browned.

For more even browning, switch the baking sheets halfway through baking.

Remove the baked quesadillas from the oven and let them cool slightly.

Use a pizza cutter to slice the quesadillas into wedges.

Serve immediately with additional cheese and sour cream, if desired.