Pound the chicken breasts to an even 1/2-inch (1.2cm) thickness. Drizzle with 1 tbsp (15ml) of olive oil. In a small bowl, combine the chili powder, cumin, kosher salt, and black pepper. Rub this seasoning blend evenly over both sides of the chicken.

Preheat a cast-iron grill pan over medium-high heat until smoking hot. Add the seasoned chicken and cook without moving for 4-5 minutes to develop distinct grill marks. Flip and cook for another 4-5 minutes until the internal temperature reaches 165°F (74°C). Remove, let rest for 5 minutes, then slice into thick strips.

Place the 1 cup (115g) of shredded Oaxaca cheese in a small non-stick skillet over medium-low heat until beautifully melted and glossy. Alternatively, melt it directly over the chicken strips in the pan during the final minute of cooking.

Slice the 2 bolillo rolls in half horizontally. Spread the cut sides with 1 tbsp (15g) of softened butter. Toast them face down in a skillet over medium heat for 2-3 minutes until a crispy, deep golden-brown crust forms.

In a small saucepan, warm the 1 cup (240g) of creamy brown refried beans over medium-low heat until hot and easily spreadable.

Spread a thick layer of the warm refried beans on the bottom half of the toasted bolillo rolls. Top with the grill-marked chicken strips, draped melted Oaxaca cheese, thick slices of fresh avocado, and overlapping pickled jalapeño rounds. Place the top bun slightly askew and serve immediately.