Preheat oven to 350 degrees. Halve the squash lengthwise; scoop out the seeds and place it in a large baking dish, cut sides down; prick the skin all over with a fork. Bake until tender, 30 to 40 minutes.

Meanwhile, in a skillet over medium-high heat, cook ground beef until browned, about 5 minutes; drain, remove from skillet and set aside.

In the same skillet, heat the oil over medium-high heat; add onion and garlic and sauté until onion is tender, about 5 minutes. Stir in tomatoes and Italian seasoning. Bring mixture to a boil then reduce heat, add cooked ground beef and simmer, stirring often, until mixture reaches desired consistency, about 5 minutes. Place Ricotta and egg substitute in a food processor or blender; puree until smooth. Coat a 9-inch glass pie plate with a little olive oil. Remove squash from oven and raise oven temperature to 375 degrees. Using a fork, carefully scrape the stringy squash pulp from the shell, separating it into spaghetti-like strands. Arrange spaghetti squash strands on the bottom and up the sides of the pie plate to form a crust.

Add Ricotta cheese mixture and gently spread over the squash. Pour tomato-ground beef sauce over the cheese mixture then sprinkle with the Mozzarella. Bake for 20 minutes. Allow the pie to stand for 5 minutes before slicing into 6 servings.