Cabernet Balsamic Burgers with Sautéed Mushrooms & Onions

Ingredients

• 5 teaspoons Celia's EVOO, divided
• 4 cups thinly sliced red onion
• 1 ½ teaspoons chopped fresh thyme
• ½ cup cabernet sauvignon or other dry red wine
• 2 tablespoons Celia's Traditional Dark balsamic vinegar
• ¾ teaspoon salt, divided
• 1 (8-ounce) package sliced mushrooms
• 1 ½ pounds ground sirloin
• Cooking spray
• ⅓ cup mayonnaise
• 1 ounce blue cheese, crumbled (about 1/4 cup)
• 1 garlic clove, minced
• 6 whole-wheat hamburger buns
• 1 ½ cups baby arugula