1. Preheat oven to 425°.
2. Sprinkle pork with pepper and salt. Heat a large ovenproof skillet over medium-high heat. Add oil to pan; swirl to coat. Add pork; cook 5 minutes, turning to brown on all sides. Place pan in oven. Bake at 425° for 8 minutes or until a thermometer registers 145° (slightly pink); let stand 5 minutes. Cut crosswise into 16 slices. Combine pork and mojo marinade in a medium bowl; toss to coat pork.
3. Combine vinegar, 3 tablespoons water, and sugar in a small saucepan; bring to a boil. Remove from heat; add onion. Let stand 10 minutes; drain.
4. Working with 1 tortilla at a time, toast in a pan or over a flame of a gas burner until tender and blackened in spots. Arrange 2 pork slices in center of each tortilla; top with about 2 tablespoons onion, 2 jalapeño slices, 2 avocado wedges, and 1 1/2 teaspoons crema.