In a Dutch oven set over medium-high heat, combine the brisket, salt, pepper, oregano, cumin, chili powder, cinnamon, onion, garlic, lime juice, orange juice, cola, and bay leaf. Partially cover it with a lid and bring to a boil, then reduce the heat to low and simmer for 3 to 3½ hours, until the meat is fork-tender, stirring occasionally to prevent sticking. If the liquid drops halfway below the meat, add enough water to just barely cover the brisket and stir to incorporate. When it’s done, remove the brisket and place it on a cutting board, reserving the braising liquid. Using two forks, shred the meat into thin strands.

In a 6-quart slow cooker, combine the brisket, salt, pepper, oregano, cumin, chili powder, cinnamon, onion, garlic, lime juice, orange juice, cola, and bay leaf. Cover and cook on low for 8 to 10 hours, or on high for 5 to 6 hours, until tender. Remove the brisket and place it on a cutting board, reserving the liquid in the cooker. Using two forks, shred the meat into thin strands.

Preheat the broiler to high and arrange a rack in the upper third of the oven. Lightly spray a sheet pan with cooking oil. Transfer the shredded beef onto the sheet pan and pour 1 cup of the reserved cooking liquid over the meat. Broil until the meat becomes browned and crispy on the edges, 5 to 10 minutes.

Season to taste with salt and pepper. Just before serving, pour more of the cooking liquid over the meat for added flavor.

Carefully char the tortillas over an open flame on a gas grill or stovetop until charred around the edges. (Alternatively, if you don’t have a gas grill or stove, preheat the oven to a high broil, place a rack in the upper third, and line a sheet pan with foil. Warm the tortillas under the broiler until slightly charred, 2 to 4 minutes.)

Spoon a few tablespoons of the brisket into the middle of each tortilla. Top with pico de gallo, cilantro, a squeeze of lime juice, and sliced avocado. Serve immediately.