Combine flour, baking powder, and salt in a large bowl. Pour in the milk and oil and mix to combine.
Form the dough into a ball using your hands. (You might need to knead it for a few minutes). Divide the dough ball into 8 equal pieces.
Heat 1/2 inch of oil over medium heat in a large skillet. Using a rolling pin, roll out each piece of dough into a circle (it doesn't have to be perfect). Pierce the surface with a fork.
Using a pair of tongs, place the dough circle into the oil and immediately fold it over to form a taco shell shape. Hold it in shape using tongs until the bottom half (that is in the oil) turns golden brown. Carefully turn it over so that the other side cooks until golden brown.
Remove the chalupa shell from the oil and place it on a wire rack to cool.
Make the Chicken
Heat 1 Tbsp. of oil over medium heat in a nonstick pan.
Combine the dry seasonings in a large mixing bowl. Toss the chicken breasts in the seasonings to coat. Pan fry the chicken until cooked through, about 7-8 minutes each side.
Remove the chicken onto a cutting board and slice thin.
Assemble the Chalupas
Spread sour cream into the chalupa shell. Follow with chicken, cheese, lettuce and tomato.