Put the onions and garlic in a large microwave-safe bowl, cover with plastic wrap and microwave at 800 watts for 2 minutes.
Let the onions cool a bit. Add the beef, panko, ketchup, soy sauce, eggs, porcini powder and black pepper. Put a glove on and knead the mixture together with your hand until uniform.
Turn the meatloaf mixture out into a non-stick loaf pan and press the mixture into the corners, flattening off the top.
Mix the ketchup and brown sugar for the glaze and then pour it on top of the meat, spreading to distribute evenly.
Cover the loaf pan with a sheet of foil and bake in the preheated oven for 25 minutes.
Remove the foil and continue baking until the meatloaf reaches an internal temperature of 145 degrees F (about another 10-15 minutes).
When the meatloaf is done, remove the loaf pan from the oven and let the meatloaf rest for 10-15 minutes.
Drain the extra fat and liquid off of the meatloaf and discard. Slice the meatloaf and serve.
