Preheat oven to 200°C. Dice the chicken breast into 2-3 cm cubes. Drain and rinse the black beans. Dice the tomatoes and onion. Shred the lettuce. Chop the cilantro. Mince the garlic. (10 minutes)

Heat the oil in a medium pot or skillet over medium-high heat. Add the diced chicken and cook for 10-12 minutes, stirring occasionally, until cooked through and lightly browned. Set chicken aside. (12 minutes)

While the chicken cooks, place the corn tortillas on a baking sheet in a single layer. Bake for 10-12 minutes, flipping halfway through, until crispy. (12 minutes)

Add the drained black beans, minced garlic, half of the diced onion, chili powder, cumin, oregano, salt, and pepper to the pot used for chicken (no need to wipe clean). Add about 50ml of water or chicken broth if you have it. Bring to a simmer and cook for 5 minutes, stirring occasionally. (5 minutes)

Mash the bean mixture with a fork or potato masher until desired consistency is reached. Stir in the cooked chicken. Cook for another 3 minutes to heat chicken through and combine flavors. (3 minutes)