Preheat the flat top griddle or a large cast iron skillet on medium-high heat.
2
Drizzle 1 tbsp of canola oil on the griddle and add the finely diced onions. Cook the onions until well caramelized, stirring occasionally with a spatula.
3
Meanwhile, season the ground beef with 1 tsp kosher salt and 1/2 tsp freshly ground black pepper, then shape into two equally sized patties.
4
Add the remaining 1 tbsp of canola oil to the griddle and place the patties on the surface. Flatten each patty with the back of a spatula, then let them cook for a few minutes.
5
Flip the patties and immediately place two slices of cheddar cheese on top of each patty to start melting.
6
While the cheese melts, spread a thin layer of mayonnaise on the inside of each hamburger bun and place them cut-side down on the griddle to toast until golden brown.
7
Place caramelized onions on top of the cheese-covered patties, then assemble your cheeseburger by stacking the patty on the toasted bun and adding your favorite condiments.