Using an electric mixer, beat cream cheese until smooth. Add yogurt, continue mixing until smooth. Reserve.
Place spinach and 2 tablespoons of water in a medium bowl. Cover with plastic wrap and microwave for 2 minutes. Allow to sit 1 minute, then drain, squeezing spinach to remove excess water. Allow to cool.
Chop spinach and artichokes. Fold into the cream cheese mixture. Add onion powder, garlic powder, salt, 1/4 cup mozzarella and Parmesan.
Cut the French bread in half. Slightly hollow each half by removing some of the bread from the middle. Fill with the spinach artichoke mixture and level the filling. Sprinkle with the remaining mozzarella.
Place the filled loaves on a baking sheet. Bake for 15-20 minutes, until the filling is bubbly and the cheese on top is browned slightly. Allow to cool for several minutes before slicing and serving.