This is a great dish for those extra tomatoes you may have.
Small tomatoes leave uncut.
Medium - large size cut in half.
Put in bowl with sliced onions and a small amount (to taste) of fresh chopped garlic cloves and toss with olive oil.
Use a baking pan with sides so juice does not spill into oven.
Roast at 400° for 45 minutes in a convection oven. Time varies per oven - so check once in a while.
You can freeze what you do not use.