Coat a nonstick 8-inch skillet with cooking spray, and preheat over medium heat. Add the mushrooms, pepper and thyme. Cover and cook, stirring several times, for about 2 minutes, or until mushrooms are tender and nicely browned. Add the spinach, and cook uncovered about 30 seconds, stirring frequently, or until spinach is wilted. Remove the mixture to a small dish, and cover to keep warm. Re-spray the skillet, and place over medium-low heat. Add the egg substitute, and cook without stirring for about 2 minutes, or until set around the edges. Use a spatula to lift the edges of the omelet, and to allow the uncooked egg to flow below the cooked portion. Cook for another minute or 2, or until the eggs are almost set. Arrange first the spinach mixture and then the cheese over half of the omelet. Top with the bacon, if desired. Fold the other half over the filling, and cook for another minute or two, or until the cheese is melted and the eggs are completely set. Slide the omelet onto a plate, sprinkle with the paprika and serve hot.