Preheat oven to 375 F. Spray a cookie sheet with non stick spray.
Cut spaghetti squash in half. Scoop out seeds. Place face down on cookie sheets. Bake for 40 minutes.
As soon as squash is cool enough to handle, scrape out the flesh with a fork.
In a saucepan, combine butter and flour. Fry until golden brown and the raw smell of the flour is gone, 2-3 minutes
Add milk, poblano and salt. Simmer for a few minutes until it thickens, about 3 minutes. Leave for 15 minutes to let the poblano infuse its flavor into the milk.
Strain and discard the poblano. Combine poblano infused milk with spaghetti squash in a large bowl and mix to combine..
Spray a casserole dish with non stick spray or grease with butter.
Add squash to buttered casserole dish. Sprinkle cheese on top. Bake for 30 minutes.