Crocks, I do something similar....
Large skillet, about 2 tbs of olive oil, 1 tbs of butter saute:
large dice vidalia or red onion
sliced or quartered mushrooms.
When onion is soft, add
sliced zucchini and yellow squash
chunks of red and orange peppers
minced garlic
parsley with some combination of basil and/or oregano
salt and pepper
When the above is half-way to "al-dente" done, reduce heat to low, add
large dice tomatoes
Cook about 5 minutes more, then sprinkle the whole thing heavily with shredded - not grated - parmesean.
Put the lid on - cocked enough to let the steam out or it will over-cook the vegetables and make the tomatoes mushy.
Soon as the cheese is melted...it's ready.
I like the flavor the butter adds to the olive oil, but I have also used less olive oil, no butter, and some good Italian dressing instead.