Preheat oven to 400 degrees.
Slice spaghetti squash in half lengthwise and scoop out the seeds.
Brush the cut side of the squash lightly with olive oil and place cut
side down in a rimmed baking dish (some liquid will escape during baking).
Bake for 30-40 minutes or until tender and easily pierced with a fork.
While squash is roasting, saute onions in olive oil over medium heat
until tender and translucent.
Season chicken with salt and pepper and add to pan. Brown meat on each side about 1-2
minutes.
Add water and half of the pesto.
Bring to a boil, cover and reduce heat to medium/low. Simmer for 25-30
minutes or until chicken is tender, adding spinach for the last 2-5 minutes to
wilt.
Remove chicken and veggies from pan with a slotted spoon, leaving the
liquid. Toss with remaining pesto.
Fluff the inside of the squash with a fork, leaving it in the shell. Top
with chicken and veggies, then sprinkle with cheeses.
Cover with foil and bake at 350 degrees for 10-15 minutes.