Pasta Al Limone con Guisantes + Espárragos

Ingredients

• 1 box Banza Spaghetti
• 1 lemon
• 1 small onion, finely chopped
• 6 oz. asparagus, trimmed and cut into 1-in. pieces
• 1 cup frozen peas
• 3 tablespoons cold, unsalted butter
• 1 cup grated Parmesan cheese
• ¼ cup torn basil leaves
• Salt and pepper
• ½ teaspoon red pepper flakes (optional)