Can I freeze freshly made spaghetti sauce, containing fresh green peppers and canned tomatoes? If so, via ziplock bag?

If you have the option, and you plan on keeping it for a significant period of time, a hard-sided container would stand up better to the freezer. Liquids and semi-liquids in ziploc bags get sharp corners when frozen, and those sharp corners have a habit of developing little holes in the plastic after being shoved around in the freezer a few times. Air gets in and you get freezer burn. I've had much better luck freezing my liquids in plastic containers.

You've cooked the sauce and cooled it down? Yes, you can freeze it in ziplock freezer bags. Double bag it if you want to keep it for a few months. Be sure to burop all the air out of the bag.

Yes keep it in a ziplock and freeze it for up I about 3 days max. But you could definitely can.