Cut the chicken into small 2-bite pieces and place in a bowl. Pour the lemon juice over the chicken to cover, and let marinate. Combine the flour, salt and yeast together for the tempura batter. Slowly mix in 2 cups cold water until you have a beautiful thick batter. Cover with a damp tea towel and let rise, 45 minutes. Remove the chicken from the marinade and pat dry. Stir into the tempura batter until the chicken is fully coated. Heat olive oil in a medium pan until hot. Fry the chicken in batches until beautifully golden on both sides, 2 to 3 minutes.