B.B.
You can not crowd the pan when making roast veggies. I find that 400-425 is the right temp for most veggies. Also, make sure you put enough olive oil or butter. Also, add salt and pepper. I love to roast cauliflower but any veggie works.
Zucchini is like egglant, it soaks up a lot of oil. You can bread them and fry them. If you still want to fry them with no breading, them you must salt them for at least an hour to remove the moisture. They taste great with homemade dill ranch dressing.
As far as the guac goes, that is the recipe but you have to remove the seeds and the wet part of the tomato before you chop it and serve it immediately since the salt draws out moisture.