Heat about 1 TBSP of olive oil in a skillet. Season the chicken with a pinch of salt and pepper, and add it to the pan, cooking it until it's fully cooked (with an internal temperature of 165º F), flipping it halfway through. Cooking time will vary depending on the cut of the chicken. I like to use chicken tenderloins since they cook quickly and shred easily; breasts or thighs will take a little longer.
Once the chicken is fully cooked, transfer it to a cutting board and dab it with some paper towels to remove excess oil. Then, with two forks, shred the chicken.
Transfer the shredded chicken, cheese, spices, onions, tomatoes, salsa, jalapeño, Greek yogurt, and a pinch of salt into a large mixing bowl, then mix everything up until the ingredients are well blended.
Line a baking sheet with parchment paper and lightly brush some olive oil over it with a pastry brush.
Put a soft taco shell onto the parchment and scoop a heaping tablespoon or two of the chicken filling onto one side of the shell. Gently press the filling down to spread it a bit over half the shell and fold the shell over. Press down on it lightly to secure it; repeat the same steps for the other tacos.
Lightly brush the tops of the folded taco shells with olive oil.
Place the tacos into the oven for about 15 minutes or until the tortillas are lightly golden and crisped at the edges.
When done, remove the tacos from the oven and let them sit for about 5 minutes to cool; serve them with salsa, guacamole, queso, and/or Plain Greek yogurt or sour cream.