Heat a large skillet over low heat. Add the olive oil and butter. Once melted, add in the onions and the salt, stirring well to coat. Cover and let cook for 25 to 30 minutes, stirring often, until golden and soft. Stir in the brown sugar and cook for another 10 minutes.

Mix all ingredients together until combined. Taste and season additionally if needed.

Whisk ingredients together until combined.

Place the ground beef in a large bowl and season with the salt, pepper and garlic powder. Mix gently to coat and then divide the beef into four equal sections. Bread apart each section and form it into two patties – one for the top and one for the bottom. Place a round of goat cheese in the center of one patty and cover it with the other patty, pressing gently around the edges to seal the goat cheese in. Repeat with remaining beef.

At this point you can grill the burgers – I chose to use the skillet that the onions were cooked in. Heat a skillet over medium-high heat and add the olive oil and butter. Cook the burgers until your desired doneness (we like medium well, at least 4 minutes per side – but remember the goat cheese is inside!), and with 1 minute before they are finished, place a few cheddar slices on top.

To assemble the burgers, spread a few tablespoons of guac on the bottom bun and place the burger on top. Cover with some caramelized onions, BBQ mayo and spring greens. Serve immediately!