Step 1Make 1/8-inch diamond cuts over surface of flank steaks on both sides. Brush both sides with lime juice.
Step 2Combine cumin, coriander, oregano and salt. Toss garlic with spices until blended. Rub spice mixture on both sides of steaks. Cover and marinate 30 minutes or up to 1 day in refrigerator.
Step 3Grill steaks over high heat to sear, 4 to 5 minutes. Turn and cook second side to desired degree of doneness, 3 to 4 minutes for rare. Remove from grill to carving board and let rest 10 minutes. Grill green onions 4 minutes, turn, and grill until hot and slightly charred, 2 more minutes. Slice steaks diagonally across grain into very thin slices.
Step 4Place each tortilla on hot grill until lightly browned, about 1 minute each side. (Can be kept warm in a cloth napkin or kitchen towel).
Step 5To serve, place a few slices of meat in center of toasted tortilla. Top with lettuce, slivered onions and Salsa Cruda. Serve each with grilled onion and lime wedge to squeeze over top.