Step 1

Place brisket in a 4- to 7-quart slow cooker and sprinkle with chile powder, cumin, 1 teaspoon salt and oregano. Whisk water and tomato paste in a small bowl and add to the slow cooker. Cover and cook on Low for 8 hours or High for 4 hours.

Step 2

About 20 minutes before serving, heat a medium skillet over medium-high heat. Add whole jalapeños and cover. Cook, shaking the pan occasionally and turning the jalapeños with tongs as needed, until charred and blistered on all sides, 10 to 12 minutes. Remove from heat and let stand, covered, for 10 minutes to soften.

Step 3

Meanwhile, prepare avocado salsa: Combine avocado, cilantro, tomatoes, sweet peppers, minced jalapeño, lime juice and salt in a medium bowl.

Step 4

Transfer the brisket to a clean cutting board. Shred it, then finely chop. Slice the blistered jalapeños.

Step 5

Serve the brisket in tortillas, with lettuce, the jalapeños, cheese and the salsa.