Start by cutting the chicken into strips or cubes and setting aside.
Cook pasta according to instructions.
Put flour into a shallow bowl or plate.
Put oil in a large frying pan.
Piece by piece coat the chicken strips and put them into the pan and sprinkle with salt and pepper (and garlic salt, optional). Cook chicken on high heat, about 5 minutes each side, then flip until both sides are browned.
Now empty cans of diced tomatoes into the pan with the chicken and about 1/2 of the feta crumbles. Stir and allow the tomatoes and feta to combine. After about 4-5 minutes the tomato sauce will start to come to a boil. Reduce heat to low, add in the spinach and fold it under the tomato sauce and chicken, it will 'wilt' as it cooks and will reduce greatly in size. When all the spinach has cooked down and the pasta is done cooking you're ready to serve.
To serve portion out pasta in a bowl and then spoon 2-3 pieces of chicken over the pasta and a few spoonfuls of sauce with the tomatoes and spinach over the pasta. Sprinkle a little of the remaining feta over the bowl and enjoy!