Here's what I do - it simulates the high direct heat and then lower, indirect to finish ( like on the real grill with multiple zones):
Put the 'grill' on the top rack (make sure its not coated or non-stick, that it can take high heat). (I do mean to put a pan under this to catch grease.)
Turn the oven to broil for a few minutes.
Prep your chicken.
Put it in the oven under the broiler for a few minutes (I can't really give you a time here because it depends on thickness and other things), but you're trying to promote that browning and a bit of char like the grill.*
After its been in a few minutes and browned/charred somewhat, pull it out and quickly flip it and repeat.
If your dish isn't fully cooked to your liking, move the item to the middle rack and turn the heat down some.
Pull it out when finished and Rest the meat.
Enjoy
To be honest though, for indoor grilling - I usually preheat the oven to 400, get some grill marks on a cast iron grill pan, and then finish in the oven. Its only when the volume is too much that I do the above method. Cast iron grill pan for a couple of servings has always been much less troublesome than the broiler which can bring items from tasty to ruined in record time for me.
*Some people close the oven door here, some don't - its the difference between if you just want to sear it or really start to cook it. I pretty nearly always close the door, but I'm also the guy who always puts the lid back on the grill.
The reason you put aluminum foil on something you bake is to block some of the heat. More specifically, you want to block the heat transfer by radiation. This is, you only want some kind of infrared-opaque shield between the heating elements and the food. Of course, it has to be also non-flammable at oven temperatures and either washable or environmentally friendly and cheap, making it one-use.
The best solution is to bake like generations of people did before there was freshly milled aluminum foil available in the supermarket: Get a clay bräter, or a tagine, or a dutch oven. Anything with a lid that is big enough to fit in your oven. Bake your food in it. It is slower, but gives you a much better taste due to slower, more even heating.
The second best solution would be to get some other stuff intended for baking, and use it as a cover. The problem is that baking paper as per Rikon's suggestion is probably not opaque enough in the infrared range - at least it is translucent in the visible spectrum. Maybe two layers of it will do, but it will get hard to work with, because it doesn't hold shape as well as aluminum foil. You could try it if you think it will help. I think that a silicone mat is more promising. It is preferable to use a light colored one of the light glossy platinum silicone - I have a black matte one which is great for rolling dough, but it will probably absorb and re-radiate too much heat.
Both solutions can't beat aluminum in one application: targeted charring protection. For a cake baked in an oven which overheats one corner there is still a chance - if your mat can be cut, you can cover half the cake with the piece (some mats shouldn't be cut because they are internally reinforced with something which shouldn't come into contact with food - if in doubt, contact the manufacturer). But if you are baking a whole bird and the protruding wings are getting overcooked, I don't see a good way to pack them in silicone or baking paper and get it to stay on them while the rest of the bird cooks. There, you will probably have to pack them in bread dough and then just break off the dough when the bird is ready.
I have never made meatloaf in a slow cooker - I didn't even know that you can bake in one - so I won't comment on that part.
Best Answer
I doubt you have melted aluminum foil at the bottom of your oven. The melting temperature of aluminum foil is 660 degrees Celsius (1,220 degrees Fahrenheit) at standard pressure. It is possible that you have a layer of grease between some foil and your oven bottom. This combination will likely char and burn. I would clean your oven well, and use as normal.