I use Furmans pizza sauce it has something like 4 carbs per serving (1/2 cup which is too much) (6-2 fiber). You don't have to use a lot of it. This is how I like mine [with the spagetti squash]
1cup of cooked spagetti squash
4-5 boneless skinless chicken breast (pounded out)
2 cloves of garlic
4 slices of onion chopped
butter
parmasean
salt and pepper

in a pan sautee the chicken in the butter along with the garlic (to brown)

Then move to a casserole first layer the browned chicken then fill the holes [that are in between each individual breast] with spagetti squash, top off with 1/2 can of tomatoe sauce and a lot of parmasean (not the stuff that comes in a can). Cover and bake at 350 for about 45min to 1hr. My family loves this. It taste like chicken caccitore (if you know what that is). Now I'm hungry again