1. Prepare the Mushrooms:

• Clean portobello mushrooms gently with a damp paper towel.
• Remove stems and gently scrape out gills.
• Mix olive oil with minced garlic and oregano.
• Brush mushrooms on both sides with the seasoned oil.
• Season with salt and pepper.

2. Make the Patties:

• In a large bowl, combine ground beef, rosemary, garlic, Worcestershire sauce, salt, and pepper.
• Mix gently with hands until just combined (don’t overmix).
• Form into 4 equal patties, making a slight dimple in the center.
• Let rest at room temperature for 15 minutes.

3. Cooking Process:

• Preheat grill or cast-iron skillet to medium-high heat.
• Grill mushrooms for 3-4 minutes per side until tender.
• Cook burger patties for 4-5 minutes per side for medium-rare (internal temperature 135°F).
• Top with feta cheese during the last minute of cooking.

4. Assembly:

• Place a grilled mushroom cap gill-side up.
• Add a handful of arugula.
• Place the cheese-topped burger patty.
• Top with sun-dried tomatoes, olives, and red onion.
• Add a dollop of Greek yogurt sauce.
• Crown with the second mushroom cap.