Calzones are surprisingly easy to make. Here is a simple method to do it completely from scratch. Just take some fat and flour or corn starch and make a roux, then dilute with stock to make a thick sauce or gravy. Add salt, pepper, and whatever other herbs and spices you like. Mix in your meat and cook well, then fill your calzones with the meat and some grated cheese.
If you keep dough in the fridge like I do, it goes together pretty quickly. I use whole wheat dough to make it healthier.
If you want something even simpler, then just take your favorite canned pasta sauce and cook some stewing beef or other chunked meat in it in a pot on the stove, and use that for your filling.