1. Cut carrots, and zucchini in similar sized pieces. Depending on the kind of squash, you may need to roast it in the oven (see recipe below). Cut onion. Mince garlic.
2. Heat pan to medium/medium high. (If using non-stick, don't preheat pan without oil.) Put 2TB olive oil in saute pan. OO has a low smoke point, so you don't want it on high or it blacken and be bitter. If this happens wipe out with paper towel. Hover your hand over the pan for a few seconds to judge that it's hot.
3. If not caramelizing onions (see recipe below), put them in first with pinch of salt to get soft. Add in carrots. Zucchini cuts pretty fast, so carrots should be tender when you put them in. Can add squash at this point.
4. Add minced garlic. Make sure it doesn't burn or it can be bitter.
5. At last minute, turn heat up to high and add 1/4 cup white wine to get up any good flavorful bits (call fond) and deglaze pan. Stir until wine evaporates. Yes, alcohol burns off.
6. Turn heat down to medium. Add tomatoes. Fresh will cook fast; canned will take 3 minutes or so.
For tomatoes, if using fresh, I'd suggest plum or grape--chopped and seeded. Cut it in half and squeeze out the seeds in the sink or separate bowl. You can use canned stewed tomatoes and break them up with flat edge spatula.
How to cut an onion:
http://www.youtube.com/watch?v=Znv46pRiDIk&list=SPB06D15EC684D362F
How to mince garlic:
http://www.youtube.com/watch?v=FSX1ALAo8wI&list=SPB06D15EC684D362F
How to saute:
http://www.youtube.com/watch?v=5LIjTp6FEbE
The saute snap:
http://www.youtube.com/watch?v=buLr3RAD5lQ&list=SPB06D15EC684D362F
(I can't do this; I just use a wooden spatula.)
Caramelize onions ahead 20-25 minutes for extra deliciousness:
http://www.epicurious.com/recipes/food/views/Winter-Squash-with-Caramelized-Onions-106292