1/2teaspooncrushed red pepper flakesreduce to 1/4 teaspoon if sensitive to spice
1cupfreshly grated part-skim mozzarella or provolone cheese divided
Chopped fresh parsley or basil
Place a rack in the center of your oven and preheat the oven to 400 degrees F. Roast the spaghetti squash according to this recipe for Roasted Spaghetti Squash. When cool enough to handle, pull the squash strings out of the squash's center with a fork and transfer to a large mixing bowl. The squash strings should look like spaghetti.
Reduce the oven temperature to 350 degrees F. Heat the olive oil in a large, deep skillet over medium high. Add the turkey, onion, bell pepper, salt, and black pepper. Cook, breaking apart the meat, until meat is browned and the vegetables are tender, about 8 minutes. Add the drained tomatoes, garlic, Italian seasoning, and red pepper flakes. Let cook until most of the liquid from the tomatoes has cooked off, about 4 minutes, and then add the reserved squash. Cook and stir until most of the remaining liquid has cooked off, about 1 to 2 minutes more, increasing the heat if needed. Stir in 1/2 cup of the shredded cheese. There may be some liquid remaining in the pan.
Lightly coat a deep 8x8-inch baking dish or 2-quart casserole dish with nonstick spray. With a slotted spoon, scoop the squash mixture into the pan in an even layer, discarding any excess liquid (some in the pan is OK—just not too much). Bake, uncovered, for 20 minutes. Remove from the oven and sprinkle with the remaining 1/2 cup cheese, and then return to the oven and bake until the cheese melts, about 5 to 10 additional minutes. For an extra-golden-brown top, place the casserole under the broiler for a few minutes. Remove from the oven, sprinkle with parsley and/or basil, and let rest 5 minutes. Serve hot.
Make it ahead: Spaghetti squash can be roasted, shredded, and stored in an airtight container for up to 3 days. When ready to make the casserole, add to the filling in Step 2 as directed.
Store leftovers in the refrigerator for up to 5 days.
I haven't tried freezing the casserole yet, but as a reader pointed out in the comments (thanks, Andrea!), spaghetti squash can get watery when thawed. If that doesn't bother you, here's what to do: Bake as directed, let cool, and then tightly cover and freeze for up to 3 months. Let thaw in the refrigerator overnight. Heat in a 350 degree F oven, covered, until warmed through. Uncover and bake 5 or so additional minutes, until hot and bubbly.
To make Paleo or Whole30 friendly: omit the cheese