Saute the squash, zucchini and onion in olive oil over medium-low heat until it has completely broken down. I like a little brown on them. *note*- Onion takes less time to cook, so add in when squash is halfway done. add salt and pepper.
When done, put squash, onion, and zucchini on a paper plate, or plate lined with a paper towel, to soak up extra oil.
while still hot, put in a buttered casserole dish, with cheese and sour cream, and mix well.
melt butter in microwave and crush the crackers in a ziplock bag.
spread the crackers evenly over the squash and cheese mixure. pour melted butter over the ritz crackers to allow crackers to brown in oven!
Bake for 25-30 minutes, or until crackers are browned but not burned!