Cook onions & chicken for a
few minutes, just until the chicken turns from pink to white.
Combine 1/2 of the spinach with the tomatoes, garlic, linquine, Italian seasoning, salt, pepper & crushed red pepper in a 5 quart Dutch oven over medium-high heat. Add chicken & onions. Pour chicken stock and wine over top. Cover and bring to a boil.
Cook 7-9 minutes until pasta is al dente (with a bite to it). Toss pasta with tongs occasionally to keep the pasta from sticking to the bottom of the pot. You will still have some liquid in the pan when the pasta is done cooking. This is going to make the base for the cheese sauce.
Turn off the heat and add the cheese to the pasta. Toss pasta with tongs until the cheese melts into the pasta. Toss in remaining spinac