Combine the ground beef with the dijon mustard, worcestershire sauce, minced garlic and black pepper. Divide equally into 8 balls. Press each ball to about 1/4" thickness .
Combine the blue cheese, cheddar cheese, and parsley flakes. Mound equally on top of 4 patties. Top with remaining 4 patties pressing edges together to create a seal.
Place patties on pre-heated grill. Alternatively, heat the oil in large skillet on medium-high heat. Cook the patties about 4 minutes, then gently turn over and cook an additional 4-5 minutes or until burgers are no longer pink. Remove from heat and top each patty with 2 TBSP pimento cheese. Serve on hamburger bun with lettuce & tomato, if desired.