Preheat grill or grill pan to medium-high. Meanwhile, heat 1 tablespoon olive oil over medium in a small skillet. Add cumin seeds and cook until toasted, 1 minute; set aside.
Rub flank steak with remaining tablespoon oil; season generously with salt and pepper. Grill, turning once, 12 to 14 minutes for medium rare. As steak grills, char tortillas on grill; set tortillas aside in a clean dishtowel as they are charred. Transfer steak to a cutting board.
Stir cumin oil together with oregano, parsley, jalapeno, garlic and lime juice; season with salt and pepper. Thinly slice meat crosswise and divide among tortillas. Spoon salsa over steak and crumble feta over tacos before serving.
Before her diagnosis, Caroline wrote a book on cakes called Cake Magic!. She started developing a birthday cake using her gluten-free mix found in that book. Check out other recipes she’s developing for her new life—and the stories behind them—on her blog, The Wright Recipes. Her next book, Catalan Food, written with chef Daniel Olivella, comes out in early September from Clarkson Potter.