Place tenderloin in a non-reactive container. Whisk together olive oil, garlic, shallots, rosemary and vinegar. Pour marinade over tenderloin and place in refrigerator for 8 hours or ovenight.
Peel and roughly chop the beets. Place in sauce pan with bay leaf, chicken stock, and salt. Simmer until beets are tender. Remove bay leaf. Place mixture in food processor and pulse leaving sauce chunky.. Remove beet sauce from blender and adjust seasoning with salt and pepper.
Heat grill. Grill tenderloin until medium rare, about 20 minutes total, turning the tenderloin to cook evenly. Let tenderloin rest for 10 minutes before slicing into 12 (4-ounce) pieces. Drizzle beef with beet sauce and sprinkled gorgonzola, serve alongside an arugula salad