Slice the chicken breasts in half, then season with pepper, salt, garlic powder, and chili powder. Using medium-low heat (about a 4 on a stovetop burner), heat a deep pan, greasing it with olive oil as it heats. Place the chicken in the heated pan, making sure they're not too crowded. Move the chicken every now and then so they don't stick to the pan. Once the white begins to creep up the sides of the chicken, flip them over and cook on the other side. Once the chicken is done, drain the fat, then remove the chicken from the pan and shred into smaller pieces. Fill a tortilla (or hard taco shell, if you prefer) with some of the shredded chicken and desired taco toppings.