The gussied-up patties at Bru Burger Bar (410 Massachusetts Ave., 317-635-4278) are bound to upset purists. One is dressed in onion gravy and Swiss cheese while another, called Mount Olympus, scales great heights with enough pepperoni, feta, fried garbanzo, red onion, marinated mushrooms, kalamata olives, lettuce, and roasted tomato dressing to anger the gods. These are hamburgers, mind you. Not subs. But in keeping with the theme of all of the projects by parent company Cunningham Restaurant Group (Boulder Creek Dining Company, Stone Creek Dining Company, Mesh on Mass, and Charbonos), Bru knew exactly what it was doing from Day One.