In a large bowl combine the ground beef, grated onion or blended onion, a beaten egg, salt and pepper. Do not overmix. Divide into 4 equal parts. I use a scale but it's not necessary. Then roll them into balls and using any flat surface like the bottom of a frying pan press them down to approximately 1 inch thick. Your hamburger patties should be slightly larger in diameter than your buns as they will shrink when cooked.
Then press an indentation in the middle of each burger with your thumb, this will keep the patties flat when cooking, otherwise they have a tendency to puff up in the middle. Arrange the burgers in a single layer on a parchment lined pan and chill them in a fridge for at least 1 hour. (This step helps patties to keep their shape on the grill.)
Grill your burgers for 5 minutes on each side. Cook time may vary depending on the level of heat from the grill. Be alert to any flare-ups from burning grease if using a BBQ. Do not press on your burgers while they are on the grill or all the juices will leak out. Add sliced cheese on top of each burger 1 minute before you take your hamburgers off the grill, cover with a lid and let the cheese melt. (If you are worried about your meat not being done, use a digital meat thermometer to check the internal temperature. It should read 160F/71C.)
In a small bowl combine the mayonnaise, ketchup and sriracha. Serve with the burgers along other toppings like lettuce, sliced tomatoes and pickles.