Saute the onion, peppers and mushrooms until soft in a saute pan with a bit of oil.
Mix the tomato sauce with everything but the meat and corn and sauted veggies.
Then put the meats, corn and veggies and wet ingredients together. Mix softly. Excessive mixing makes the meat tough. The gelatin will act to solidify the meat and when you cut it, it won't break up into a mess.
Take a loaf pan and line with Saran wrap, leaving a generous amount over the sides. Pack in the meatloaf and then pull the wrap to cover. Place in the fridge for at least two hours.
Preheat oven to 400-425. Take a roasting pan and line with foil. Get the meatloat, pull back the wrap and place a finely wired rack on top. Then invert, and place the rack in the baking dish.
Slide off the loaf pan and pull off the saran wrap. Place in oven for 1 hour.
Remove from oven, and with a metal spatula, losen and slide to a serving plate. Meatloaf is free of any grease and is nicely crusted on all sides.
Feel free to add any other ingredients you like or subtract any, except the unflavored gelatin. This is more about technique than ingredients.