Melt butter in large skillet. Add zuchini, squash, and onion. Saute over medium heat, about 20 minutes, or until tender, adding whatever seasonings you prefer. (I like to use Mrs. Dash Lemon and Pepper seasoning, and some kosher salt.)
Reduce heat to low. When vegetables are tender, carefully stir in tomatoes and 1 c. of the cheddar cheese. Cook, stirring occasionally, until cheese melts. Sprinkle remaining c. of cheese on top. Cook until melted. Serve immediately. Enjoy!