Pre-cook zucchini to add to spaghetti sauce?

I am making spaghetti and meat tonight for the first time! We usually just have spaghetti with meat sauce. The recipe for the meat has you bake them so I was just going to add them to my heating sauce after they are cooked. I want to add some zucchini to get some veggies in there. Would it be best to add the zucchini when I very first heat the sauce so they will have time to get tender or should I steam it first to make sure it is tender. My hubby and daughter will not eat if its still crunchy at all. What do you think??? Any advice welcome!