Combine first 4 ingredients and 1/4 teaspoon salt, stirring well. Set aside.
Sprinkle steak with chili powder, oregano, and remaining salt. Heat oil in a large nonstick skillet over high heat. Add steak and green pepper; sauté 2 minutes or until meat is done and pepper strips are tender.
Warm tortillas according to package directions. Spoon about 3/4 cup steak mixture down center of each tortilla. Top each with 1/2 cup spinach and 2 tablespoons yogurt mixture. Sprinkle with black pepper; roll up. Serve immediately.