Combine the lamb, grill seasoning, fennel seeds, oregano, cumin and crushed red pepper. Form into four patties.
In a large skillet, heat the EVOO, one turn of the pan, over medium-high heat. Add the patties and cook, flipping once, for 3 minutes on each side for medium-rare doneness.
Using a food processor fitted with a grating disk, grate the cucumber and garlic. Add the yogurt, feta and lemon juice and puree to make a tzatziki sauce.
Spread some tzatziki sauce on the roll bottoms and top with the burgers, lettuce, tomato, red onion, more sauce and the roll tops. Serve with the potato chips alongside.