Make the burger sauce

• In a small bowl, combine 2 tbsp mayo, 1 tbsp ketchup, 1 tbsp yellow mustard, 1/2 tsp black pepper, salt and garlic powder.
• Stir in 1 tsp grilled onions and 1 tsp relish.
• Mix well and set aside.

Caramelize the onions

• Heat 2 tbsp olive oil and 1 tbsp butter in a skillet over medium heat.
• Add the diced onion and cook until soft and golden.

Make the garlic butter

• Melt 2 tbsp butter.
• Stir in the 2 minced garlic cloves and chopped parsley.
• Mix and set aside.

Smash the burgers

• Heat a little avocado oil in a hot skillet or griddle.
• Divide the ground beef into 4 balls and season with burger seasoning.
• Place the balls in the pan and smash them flat with a spatula.
• Cook until a crust forms, then flip.

Melt the cheese

• Place a slice of cheddar on each patty.
• Let it melt completely.

Toast the croissants

• Brush the cut sides of the croissants with the garlic butter.
• Toast them in the pan until golden and fragrant.

Assemble

• Spread burger sauce on the bottom croissant half.
• Add lettuce, tomato, the cheesy patty and grilled onions.
• Top with more sauce and close with the croissant top.
• Serve immediately.