Put a cold frying pan on the burner and don't turn it on. Put 2 tablespoons of oil in bottom of pan. Put chicken tenders in pan. Sprinkle salt and/or pepper over the chicken. Sprinkle flour over the chicken, as thick or thin as you like. Flip the chicken over and repeat. Turn on stove on about medium/low heat, depending on your stove. When chicken is browned on one side, flip over and cook the other side. Remove chicken from pan and set aside if you want your chicken crispy, with the lemon sauce on the side. Or keep in the pan if you want the chicken to absorb the lemon sauce. If you have a good amount of oil and cooked flour/breading in the pan, you don't need to do anything. If you don't have enough, add more. Usually there is plenty of oil, but you may need more flour so your sauce isn't too oily and thin and it's a lot easier to add the flour now. If you added flour, stir it around to absorb the oil. Pour the chicken stock and lemon juice into the pan and bring to a simmer. Let simmer for 2-3 minutes, or until sauce has reduced by half and thickened. Check seasonings and add more salt, if desired. Turn off the heat and stir in the butter. Add lemon slices and chopped fresh parsley to the pan to garnish.