G.B.
I can't imagine the ingredients you've listed. I don't think meatloaf and mushrooms or grape tomatoes go together nor do you fix it like a pot roast.
Most meatloaf's have meat, egg, tomato sauce, onion, sometimes some flaked red peppers, and stuff like that. It's a savory meat with lots of Catsup or Ketchup.
Meat loaf produces a ton of grease so everything you place around it is going to be floating in grease. It is supposed to sort of dry out on the top so the ketchup topping is cooked down a bit. Covering it will make it runny and not cook well.
I suggest you look up a recipe that is similar to what you want to make. I use Cottage Meat Loaf for my recipe. The kids like that the sauce is sweet due to the brown sugar in it. It's a very good meatloaf.
If you go ahead and make it like this I suggest you put the veggies in as soon as the meat goes in but I wouldn't put them in there at all, all that blood is going to ooze out and it cooks in the bottom of the pan in the grease.....