Cook spaghetti according to package directions.
Meanwhile, in medium bowl, beat eggs. Add sour cream, Parmesan and garlic powder.
Drain spaghetti and add to egg mixture with Monterey Jack, spinach and half the onions.
Pour into greased 9x13” pan. Cover and bake at 350 degrees for 30 minutes or until heated through.
Top with remaining onions and return to oven and bake uncovered 5 minutes or until onions are golden brown.