Cut tofu into 1-inch thick slices. Drain. Set them on a sheet, cover with another baking pan or cookie sheet and weight down with something heavy; drain for at least 1/2 hour to remove excess water. In a small cast iron skillet toast cumin, chili and oregano until they emit a lovely aroma. Remove to a nonreactive saucepan and add olive oil, garlic, vinegar and white wine. Bring to a simmer. Transfer drained and weighted tofu to a flameproof ceramic dish and pour marinade over tofu. Cover with plastic and refrigerate for a day at least or, for up to 3 to 4 days. Preheat the broiler. Remove marinated tofu, pat dry and broil, about 6 inches away from the heat until crispy on each side. Spread bread with mayonnaise; slice tofu in half to make 1/2-inch slices and set over mayonnaise. Top with tomato, arugula and onion if you wish. Spread second slice of toasted bread with chili mayo and cover sandwich.