1. Heat a large skillet over medium heat. Add oil to pan; swirl to coat. Add fennel, onion, 1/4 teaspoon salt, and 1/4 teaspoon black pepper; cook 5 minutes or until tender, stirring occasionally. Cover; cook over low heat for 10 minutes or until fennel mixture begins to brown, stirring occasionally. Uncover; cook 10 minutes or until mixture is golden and caramelized. Remove from pan; keep warm.
2. Combine remaining 1/4 teaspoon salt, remaining 1/4 teaspoon black pepper, white pepper, coriander, and red pepper in a small bowl. Rub mixture evenly over beef. Wipe skillet clean with a paper towel; return skillet to medium-high heat. Lightly coat beef with cooking spray; add to pan. Cook 4 minutes on each side or until desired degree of doneness. Let stand 5 minutes; thinly slice.
3. Combine Swiss chard and lemon juice, tossing to coat.
4. Working with 1 tortilla at a time, toast tortillas in a pan or over the flame of a gas burner until tender and blackened in spots. Arrange 1/4 cup chard mixture in center of 1 tortilla; top with about 1 ounce beef and 2 tablespoons fennel mixture. Repeat with remaining tortillas, chard mixture, beef, and fennel mixture. Top each with 1 teaspoon crema.