Bavette is the French term for a cut of beef that's known in English by the unappetizing name of flap steak. Bavette is tougher and more fibrous than some of the more popular cuts, but it's full of flavor and cheaper than similar cuts such as flank and skirt. Bavette is best suited for cooking quickly over a high, dry heat -- grilling and stir-frying are good techniques to use. Marinate first, never cook further than medium rare, then slice against the grain for best results.
Combine the garlic, ancho chili powder, oregano, salt, pepper and olive oil in a bowl and whisk together until well combined. This is your marinade.
Place the bavette steaks in a shallow nonreactive dish and pour the marinade over the meat. Cover with plastic wrap and refrigerate overnight.
Remove the meat from the refrigerator approximately an hour before cooking and let it return to room temperature.
Prepare your gas or charcoal grill in the meantime. You will want the fire to be medium-hot. Hold your hand palm down just above the grill rack and count how many seconds it takes before you have to remove your hand. You're aiming for 3 seconds for medium-high.
Remove the meat from the marinade and pat dry with paper towels. Season with more salt and pepper.
Grill over direct heat for about six minutes per side, until medium rare.
Let the meat rest for about five to 10 minutes, then cut against the grain into thin slices. Serve immediately.