Epic Burger with Chimichurri and Plancha Grilled Cheese - Girls Can Grill

Ingredients

• Red onion (thinly sliced)
• 1/4 cup olive oil (divided)
• 1 tbsp sea salt (divided)
• 6 tomato slices
• 2 lbs ground beef (80/20)
• Sea salt
• 6 brioche buns
• 6 1/2-inch thick slices provolone cheese
• Yellow mustard
• 3 cloves garlic
• 2 tbsps shallot (diced)
• 1/2 serrano pepper (seeds removed)
• 1/2 cup fresh cilantro
• 1/2 cup fresh parsley
• 2 tbsps fresh oregano
• 1/4 cup red wine vinegar
• 1/2 cup olive oil
• 1 1/2 tsps sea salt