Spray a large skillet with cooking spray and set to medium-high heat. Sauté onion until edges are light brown, about 7-9 minutes. Reduce heat to medium and add ground beef and salt, breaking up beef and sautéing about 5 minutes until browned.
Turn heat off, remove pan from heat and stir in chilis, cheese and Greek yogurt.
Place half of the tortillas in between two paper towels and heat for 30 seconds until they are warm and pliable. Repeat for the other half of the tortillas. Now you're ready to roll up the taquitos!
Carefully put 2 tablespoons of beef filling in a line down one side of a wrap. Roll the wrap up tightly, and place seam-side-down on a baking sheet that's been sprayed with nonstick spray. Repeat for the rest of the tortillas. Place each a half inch apart from each other on the baking sheet, so they can get toasted on all sides. Give all taquitos a light mist of cooking spray (or brush with olive oil) before putting in the oven.
Bake at 425º for 10 minutes. Remove from the oven and serve with your favorite salsa or pico de gallo!