Panfried Burgers Stuffed with Blue Cheese

Name: Panfried Burgers Stuffed with Blue Cheese
Ingredients: 8 thick slices coarse country bread; 2 Tbs. extra-virgin olive oil; Sea salt and freshly ground pepper; 2 garlic cloves, halved crosswise; 1 1/2 lb. (750 g) ground beef chuck (20 percent fat); 1/2 tsp. garlic powder; Kosher salt and freshly ground pepper; 1/4 lb. (125 g) very cold blue cheese, cut into 4 thin slabs, plus crumbled cheese for serving (optional); Olive oil for brushing; Sliced red onion and sliced tomato for serving (optional); Mayonnaise, ketchup or mustard for serving (optional)