Apologies, I did not see your reply sooner! I basically cut the tomatoes into quarters along with an onion and bell pepper(s) plus halved jalapenos/any other peppers depending on how spicy you want it. Add a head of garlic too with the top cut off. Spread all of these veggies on a foiled cookie sheet, drizzle with olive oil, and roast in the oven at ~450F for 20-30 min until the edges start to brown. Then let it cool a little and blend it up, adding lime/lemon juice, salt, pepper, cumin, and cilantro to taste.

What's nice is you can roast whatever you have on hand, and it comes out slightly different each time. You can jar it for longer storage as well :)