Spray a large skillet with cooking spray. Turn heat to medium high.
Cook the onion and squash in 1/2 cup water, stirring frequently until the onion is translucent and the water is completely evaporated.
Lower the heat to low, and add 1/4 cup cheddar cheese, yogurt, parmesan cheese, seasonings and milk. stir until well combined. Turn off heat.
Scoop everything into a blender, and blend until smooth.
Meanwhile, cook the pasta according to package directions, and drain in a colander, (don't rinse pasta). Add pasta to the skillet, and pour cheese sauce over warm pasta. Stir until pasta is coated with cheese sauce, and stir in additional 1/4 cup cheddar cheese.* (Add an additional 1-2 tbs milk if you want it more creamy.) *Serve warm!