Roasted Lemon Chicken with Spring Onion Chimichurri

Name: Roasted Lemon Chicken with Spring Onion Chimichurri
Ingredients: 2 lemons; One 4- to 5-pound whole chicken; Kosher salt and freshly ground black pepper; 4 sprigs fresh tarragon; 3 cloves garlic; 1 tablespoon unsalted butter, melted; 1 1/2 cups loosely packed fresh flat-leaf parsley leaves; 2 tablespoons fresh tarragon leaves; 3 spring onions, dark green parts trimmed off and bulbs roughly chopped; 1 small clove garlic; 1/2 cup olive oil; 2 tablespoons champagne vinegar; 1 pinch crushed red pepper flakes; Kosher salt